Design, Synthesis and Biological Evaluation of Highly Potent Simplified Archazolids.

The archazolids are potent antiproliferative compounds that have recently emerged as a novel class of promising anticancer agents. Their complex macrolide structures and scarce natural supply make the development of more readily available analogues highly important. Herein, we report the design, synthesis and biological evaluation of four simplified and partially saturated archazolid derivatives. We also reveal important structure-activity relationship data as well as insights into the pharmacophore of these complex polyketides.

Introduction

Extended polyene segments are key structural features of a broad range of complex polyketide macrolide antibiotics. The archazolids A (1) and B (2, Figure 1) are typical representatives which were first reported in the 1990s by the Höfle group as a novel class of highly potent antiproliferative agents.1 A decade later, Sasse et al. and Huss et al. reported V‐ATPase as a molecular target inhibited by archazolids,2, 3 and subsequently, the binding site has been defined.4, 5 In 2011, archazolid F (3), was demonstrated to display higher antiproliferative activity making it the most potent member of this family.6 In recent years, the archazolids have also been shown to exhibit remarkable inhibitory effects of tumor growth, and based on these studies they have emerged as a promising class of novel anticancer drugs.7, 8, 9, 10, 11, 12 Furthermore, the G protein‐coupled A3‐adenosine receptor, the ATP‐gated ion channel receptor P2X3, and human leukocyte elastase have been discovered as further molecular targets of archazolids, which may contribute to their anticancer activities.13

Figure 1

Potent members of the archazolid family.

The archazolids are 24‐membered macrolactones with eight stereocenters, 7 double bonds and a thiazole side chain. As they are only produced in scarce quantities by nature, there is a need for a synthetic approach to provide sufficient amounts for studies on their mode of action and their target selectivity. So far, one total synthesis of archazolid A was published by us in 2007,14 and two total syntheses of archazolid B have been reported by the Trauner group15 and our group in 2007 and 2009.16 In 2018, we accomplished the total synthesis of archazolid F.17 Furthermore, elaborate fragment synthesis of 2,3‐dihydroarchazolid was published by O'Neil et al.18, 19, 20

Design of new simplified archazolid derivatives

Despite various total syntheses, only few SAR studies have been published so far, relying on compounds obtained by chemical derivatization of natural archazolid A21 or on acyclic fragments.21, 22 Initial archazolid derivatizations mainly occurred on the two free hydroxy groups as well as on the carbamate side chain. In detail, modification of either hydroxy function led to a drop in potency,21 whereas removal of the carbamate side chain had only a minor effect on biological activity.22 Hence, it was proposed that the northern part would be critical for binding, as shown in Figure 2. This hypothesis was further supported by docking calculations and molecular dynamics experiments.23 Accordingly, a novel synthetic route towards such macrolides was developed and applied for the total synthesis of archazolid F.17 This strategy relied on disconnections of the C18–C19 bond, by an aldol condensation and a ring closing metathesis along the C3–C4 bond. The synthetic methodology route was subsequently used for the total synthesis of a first series of unnatural analogues.13 The substantially simplified analogue 4 (Figure 2) was discovered which still exhibited excellent antiproliferative activity towards several mammalian cancer cell lines, even surpassing the activity of natural archazolid F. These results confirmed our previous hypothesis that the archazolids’ binding site is located in the northern, top part of the macrolactone.

Figure 2

Proposed pharmacophoric area of the archazolids leading to the design of potent archazolog 4 6 and further simplifications addressed within this study.

Based on the structure of analogue 4, a further series of derivatives was devised for this study, focusing on additional simplifications of the southern part. Modifications were gathered around saturations of the three double bonds C3–C4, C5–C6 and C20–C21 as well as the elimination of the C5 methyl group. Loss of these double bonds would introduce more flexibility into the macrocycle and also shorten the synthetic route. Removal of one double bond could indicate its relevance for biological activity. Based on this rationale, the four derivatives 5–8 (Figure 3) were envisaged.

Figure 3

Targeted analogues of this work and their retrosynthetic analysis.

Results and Discussion

The synthesis of these derivatives uses a methodology developed during the total synthesis of archazolid F.17 As shown in Figure 3, the implementation of the analogues 5–8 was achieved by the combination of two fragments, that is, a main northern subunit of type 10 and various southern segments of type 9. Following our own precedence,17 an aldol‐condensation sequence was planned to forge the 18,19‐double bond, while a novel macrolactonization approach was considered to close the ring.

Schemes 1, 2 and 3 show the synthesis of the main fragments 27, 28, 39 and 40 by robust and reliable routes involving aldol and olefination reactions that have previously been established on related systems.14, 16 As shown in Schemes 2 and 3, we first focused on the preparation of the main fragments 27 and 28, which were required for analogues 5 and 6. Their synthesis started with ketone 12 which was obtained in four steps from commercially available pentandiol 11 (Scheme 1). C2 homologation was initially attempted with Wittig ylide 13 a (Table 1) which was found to be too unreactive to produce ester 14. On the contrary, Horner‐Wadsworth‐Emmons (HWE) reagents such as 13 b and c were more appropriate. Although rather low yields and selectivities were obtained using NaH or Potassium bis(trimethylsilyl)amide (KHMDS; Table 1), BuLi was found to result in higher degrees of conversion but still low selectivity. The presence of a bulkier R group on the phosphonate was described to increase the selectivity.24 However, in our case with phosphonate 13 b, the E/Z ratio was only slightly improved from 2 : 1 to 3 : 1. The best conditions involved the use of phosphonate 13 c and the addition of N,N′‐dimethylpropylene urea (DMPU) in combination with BuLi at room temperature with prolongated reaction times overnight, resulting in a high yield (80 %). At this stage, the selectivity of 3 : 1 was accepted as the two isomers were easily separated by column chromatography. Finally, the resulting enoate 14 was converted to aldehyde 15 in two steps. This route proved to be scalable and employed inexpensive starting materials.

Scheme 1

Synthesis of aldehyde 15.

Scheme 2

Synthesis of main fragments 27 and 28.

Scheme 3

Synthesis of main fragments 39 and 40.

Table 1

Olefination reactions of ketone 12.

Reactants	Conditions	Yield[a]	E/Z
12+13a	CH2Cl2, reflux, 24 h	–[b]	–
12+13a	toluene, reflux, 24 h	–[b]	–
12+13c	NaH, THF, RT, 24 h	16 %	2 : 1
12+13c	KHMDS, THF, RT, 24 h	36 %	2 : 1
12+13b	nBuLi, THF, RT, o/n	52 %	3 : 1
12+13c	DMPU, nBuLi, THF, RT, o/n	80 %	3 : 1

[a] Combined yield. [b] No conversion.

–

–

As shown in Scheme 2, aldehyde 15 was then subjected to a boron‐mediated Paterson aldol reaction with the (S)‐lactate‐derived ketone 16,25 which proceeded with excellent yield and diastereoselectivity (dr>20 : 1) towards β‐hydroxyketone 17. After tert‐butyldimethylsilyl (TBS) protection, LiBH4 reduction and cleavage of the diol with NaIO4, aldehyde 18 was obtained. The Z/Z/E triene was then generated using two consecutive Still‐Gennari reactions and an HWE olefination with excellent yield and selectivity. After reduction and oxidation of ester 24, the required building block 27 was obtained by a syn‐boron‐mediated aldol reaction with diethyl ketone 26 26 and TBS protection. For the synthesis of analogue 5 (see below), the tert‐butyldiphenylsilyl (TBDPS) group had to be replaced by a triethylsilane (TES) group. Accordingly, the primary hydroxy group of 27 was selectively liberated in presence of the two secondary TBS groups using tetrabutyl ammonium fluoride (TBAF)/AcOH conditions27 and reprotected as a TES ether towards 28.

The more simplified main fragments 39 and 40 which lack the C2–C3 and C4–C5 double bonds as well as the C5 methyl group as required for archazologs 7 and 8 were prepared in an analogous manner (Scheme 3). In detail, both the corresponding Paterson aldol coupling with derived aldehyde 30, the two consecutive Still‐Gennari olefinations with aldehydes 32 and 34, as well as the HWE‐olefination with 36 and the final Ipc‐mediated boron aldol reaction of 38 proceeded with excellent selectivity, giving the required chiral triene building block 39 in an effective and scalable fashion. Likewise, all intermediate interconversions, mainly involving adjustments of the required oxidation states of 31, 33, 35, and 37 could also be carried out in reliable fashions and high yields. The corresponding TES ether 40 was prepared again by the facile deprotection/reprotection sequence.

With these northern fragments in hand, efforts were directed towards the pivotal aldol condensation sequence to access the fully functionalized carbon skeleton of the desired analogues (Scheme 4). The required aldehyde 41 was obtained from the corresponding diol by mono‐acetate protection and Swern oxidation, while 42 was prepared from but‐3‐en‐1‐ol28 by cross metathesis with acrolein and TBS protection. Gratifyingly, a three step aldol‐condensation sequence could be implemented, which proceeded with excellent selectivity as well as good yield. In particular, full degrees of conversions of the starting ketones 27, 28, 39 and 40 in the initial aldol coupling were obtained with lithium tetramethylpiperidine (LiTMP). Indeed, it was found that LiTMP offers the double benefit of full conversion and facile work‐up in contrast to Ph2NLi used in the total synthesis of archazolid F.17. Acetate esterification of the aldol products and a 1,8‐Diazabicyclo[5.4. 0]undec‐7‐ene (DBU)‐mediated elimination then afforded the desired unsaturated ketones 43 a/b–44 a/b. Excellent E selectivity was obtained in the final elimination step by careful temperature control in the initial aldol reaction. Indeed, an increase of the temperature over −30 °C during the enolate formation resulted in an approximately 3 : 1 E/Z mixture after the elimination step to 43 a and 43 b.

Scheme 4

Coupling of the main fragments by an aldol‐condensation sequence.

As shown in Scheme 5, for completion of the synthesis, ketones 43 a/b and 44 a/b were selectively reduced by means of NaBH4. This procedure was originally described by the Trauner group15 in their total synthesis of archazolid B and had subsequently also been used by us in the preparations of archazolid F17 and related analogues.13 Gratifyingly, this protocol again proceeded with good selectivity (dr 10 : 1) and yields to give, after methylation with Meerwein salt, the corresponding ethers 47 a/b and 48 a/b. The protecting group at the C1 hydroxy group was then selectively removed under TBAF/AcOH conditions for the TBDPS groups of 47 a and 47 b and K2CO3 for the TES groups of 48 a and 48 b. The primary alcohols were then oxidized to the carboxylic acids in two steps applying the Parikh‐Doering and Pinnick procedures. The C23 hydroxy protecting groups were selectively removed with K2CO3 for the acetate groups (Scheme 5, left) and HF‐pyr for the primary TBS groups (right) affording the corresponding alcohols 47 a/b and 48 a/b. Deprotection at the C1 hydroxy group as well as the two oxidations to the carboxylic acids proceeded smoothly while deprotection of the C23 positions was less satisfying (40‐50 % yield). The macrocycles were then closed using the Shiina macrolactonization method. Slow addition of the seco acids to a highly diluted solution of 2‐methyl‐6‐nitrobenzoic anhydride (MNBA) and 4‐dimethylaminopyridine (DMAP), pretreated with 4 Å molecular sieves, led to the formation of the macrolactones with high yield (77–86 %), without side products and the need of HPLC . Notably, these cyclizations represent the most efficient methods for macrolide formation of the archazolids reported so far. The reported ring closing methods for the archazolids are so far a HWE macrocyclization (Arch A: 44 %), a Hoye relay ring‐closing metathesis (Arch B: 27 %), a Heck coupling (Arch B: 60 %: diastereomeric mixture) and a RCM reaction (Arch F: 49 %). Finally, global deprotection of the secondary TBS groups successfully afforded the four targeted derivatives 5–8. Similar to the C23 deprotection, removal of the secondary TBS groups was difficult (25‐40 %) and required prolonged reaction times as well as subsequent additions of HF‐pyr to realize full conversion.

Scheme 5

Completion of the synthesis of analogues 5–8 by macrolactonization.

Importantly, the choice of protecting groups on the two primary alcohols at C1 and C23 was found to be crucial for the successful synthesis of 5 and 7. For these two analogues, carrying the C20–C21 double bond, the C23 hydroxy group, prone to elimination during the aldol‐condensation sequence, had to be equipped with a carefully chosen protecting group. The C1 protecting group had to be orthogonally deprotectable with respect to C7, C15 and C23, whereas C23 itself had to be deprotected without affecting the protection of C7 and C15.

As shown in Table 2, several strategies were evaluated. Primary attempts with a benzoic ester functionality (entry 1) as protecting group led to a formation of the C18–C23 triene during the DBU‐mediated elimination. The aldol condensation sequence with PMB as R2 (entry 2) led to the desired diene with good yield. Deprotection occurred with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ); however, only low yields were obtained, and oxidation at C17 was also observed. Attempts to reduce this group at a later stage of the synthesis were also carried out but could only be realized in low yield. The other variable on the molecule was the protecting group at C1. Removal of the TBDPS group to directly introduce the carbonate functionality (entry 3) led to degradation of the ketone during the aldol reaction. Similar degradation was observed with an acetate group as R1 (entry 4). The best combination was found to be a TES group as R1 and a TBS group as R2 (entry 5). Indeed, the TBS group suppressed further elimination along the 22,23‐bond during the aldol‐condensation sequence and the TES group was selectively cleaved in the presence of three TBS groups with high yield. After oxidation at C1, the primary R2‐TBS ether could be successfully removed without affecting the two secondary TBS groups using a diluted solution of HF‐pyr.

Table 2

Crucial protecting groups choice for the precursors to 5 and 7.

	Protecting groups	Aldol condensation	R1/R2 deprotection
1	R1=TBDPS, R2=Bz	elimination	/
2	R1=TBDPS, R2=PMB	61 %	79 %/31 %
3	R1=CO2Me, R2=TBS	degradation	/
4	R1=Ac, R2=TBS	degradation	/
5	R1=TES, R2=TBS	60 %	94 %/42 %

/

/

/

All four new analogues 5–8 retained antiproliferative activities against 1321 N1 astrocytoma cells in the low‐nanomolar range similar to the parent natural product archazolid F (Table 3). However, they did not reach the sub‐nanomolar potency of archazolog 4. Macrolactones 5–8 also showed similar human P2X3 receptor inhibition as compared to 4. Our results demonstrate that removal of the (3,4), (5,6) and (20,21) double bonds as well as the C‐5 methyl group are well tolerated with almost no change in activities in these assays. These data confirm and refine our pharmacophore model and demonstrate that the overall structure may be further simplified without loss of biological activity.

Table 3

Biological data of novel analogues 5–8 in comparison to archazolid F (3) and archazolog 4.

	3	4	5	6	7	8
Growth inhibition of 1321 N1 astrocytoma cells IC50±SEM [nM]	4.51±0.51	0.757±0.121	12.2±2.9	19.6±4.0	9.65±1.48	17.4±1.30
Human P2X3 inhibition IC50± SEM [μM]	0.438± 0.144	1.31±0.19	2.46±0.46	1.19±0.18	1.02±0.24	1.87±0.03
Affinity for the human adenosine A3 receptor K i±SEM [nM]	859±75	690±39	539±44	436±111	>1000	>1000
HLE inhibition K i±SEM [μM]	0.830±0.134	5.85±0.16	5.01±0.79	13.3±1.5	5.78±0.65	8.18±1.01

In contrast, the modifications addressed within this study did influence the affinity to the A3 adenosine receptor. In detail, the (5,6)‐olefin in combination with the appending methyl group was crucial for receptor interaction, as analogues 7 and 8 lacking this functional pattern were inactive. In contrast, new analogues 5 and 6, retaining these structural features were still potent and even exhibited slightly better affinity as compared to archazolid F. These results are in agreement with an earlier study6 demonstrating that also slight variations in the C2–C3 region had a profound biological effect on this target. In summary, these results suggest that the eastern part of the archazolids is involved in A3 adenosine receptor binding. Regarding human leukocyte elastase (HLE), the new archazologs retained moderate inhibitory potency at this enzyme, but were weaker than archazolid F.

Conclusions

In conclusion, we have reported the design and synthesis of four novel partially saturated archazolid derivatives and their biological evaluation. The design of these derivatives is based on previous SAR studies and pharmacophore analysis suggesting the archazolids’ binding site to be located on the top part of the macrolactone. The modifications were focused on the C3–C4, C5–C6 and C20–C21 double bonds as well as the C5 methyl group. The synthesis relied on a scalable and convenient approach to the northern part utilizing an olefination and aldol methodology as well as a coupling with various southern fragments using a highly stereoselective aldol condensation sequence. We report for the first time the implementation of a macrolactonization strategy to close the archazolid 24‐membered ring without formation of any side product such as dimers. Further insights into the archazolids’ pharmacophore were obtained after biological assessment of these new analogues. Indeed, derivatives 5–8 retained potent antiproliferative activities in the nanomolar range, similar to the parent natural product archazolid F but weaker than archazolog 4. The modifications of these analogues were well tolerated by the P2X3 receptor and HLE as demonstrated in inhibition assays suggesting that further simplifications might be allowed. However, the results of the A3‐adenosine receptor binding assays showed that modifications in the C3–C6 area led to a drop in potency suggesting the crucial role of this pattern for receptor interaction. The developed synthetic approach allowed easy access to simplified archazolid derivatives and could be used to further develop this promising novel class of potent anticancer drugs.

Experimental Section

General procedures. All reagents were purchased from commercial suppliers (Sigma‐Aldrich, TCI, Acros, Alfa Aesar) in the highest purity grade available and used without further purification. Anhydrous solvents (CH2Cl2, Et2O, THF, and toluene) were obtained from a solvent drying system MB SPS800 (MBrain) and stored over molecular sieves (4 Å). The reactions in which dry solvents were used were performed under an argon atmosphere in flame‐dried glassware, which had been flushed with argon unless stated otherwise. The reagents were handled using standard Schlenk techniques.

Thin‐layer chromatography monitoring was performed with silica gel 60 F254 precoated polyester sheets (0.2 mm silica gel, Macherey‐Nagel) and visualized using UV light and staining with a solution of CAM (1.0 g Ce(SO4)2, 2.5 g (NH4)6Mo7O24, 8 mL conc. H2SO4 in 100 mL H2O) and subsequent heating.

Semipreparative and analytical HPLC analyses were performed on Knauer Wissenschaftliche Gerate GmbH systems. The solvents for HPLC were purchased in HPLC grade. The products were detected by their UV absorption at 230 or 254 nm, respectively. All NMR spectra were recorded on Bruker spectrometers with operating frequencies of 125, 150, 500, 600, and 700 MHz in deuterated solvents obtained from Deutero. Spectra were measured at room temperature unless stated otherwise, and chemical shifts are reported in parts per million relative to (Me)4Si and were calibrated to the residual signal of undeuterated solvents.29 For full assignment of 1H and 13C signals of the final products, see the supporting information section. Optical rotations were measured with a PerkinElmer 341 polarimeter in 10 mm cuvette and are uncorrected. High‐resolution mass spectroscopy (HRMS) spectra were recorded on a Thermo LTQ Orbitrab Velos mass spectrometer.

General method A: Paterson aldol reaction. To a solution of chlorodicyclohexylborane (1.00 equiv) in Et2O at −78 °C, was added DMEA (2.0 equiv) followed by ketone 16 (1.00 equiv) in Et2O. The reaction was stirred for 2 h at 0 °C then cooled down again at −78 °C. The aldehyde (1.10 equiv) in Et2O was added. The mixture was stirred for 1 h at −78 °C and then stored at −20 °C overnight. The reaction was quenched at 0 °C with MeOH, pH 7 buffer and H2O2 (2 : 2 : 1) and stirred for 1.5 h at room temperature. After separation of the organic phase, the aqueous phase was extracted with CH2Cl2. The combined organic layers were dried over MgSO4, evaporated in vacuo and purified by column chromatography.

Ketone 17: Method A with chlorodicyclohexyl borane (10.1 mL, 10.1 mmol), DMEA (1.45 mL, 13.4 mmol) in Et2O (55 mL), ketone 16 (1.43 g, 6.69 mmol) in Et2O (50 mL) and aldehyde 15 (2.86 g, 7.35 mmol) in Et2O (4 mL). Work‐up MeOH (10 mL), buffer (pH 7, 10 mL), H2O2 (5 mL) and CH2Cl2 (3×50 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 17 (3.23 g, 5.50 mmol, 82 %, dr>20 : 1). R f=0.31 (SiO2, CH/EtOAc, 5 : 1); [α] =+18.0° (c=0.44, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=8.13–8.10 (m, 2H), 7.70–7.67 (m, 4H), 7.60 (ddt, J=7.9, 7.0, 1.3 Hz, 1H), 7.49–7.37 (m, 8H), 5.48 (qd, J=7.0, 1.6 Hz, 1H), 5.13 (dq, J=9.3, 1.3 Hz, 1H), 4.60 (td, J=9.0, 4.3 Hz, 1H), 3.68 (t, J=5.9 Hz, 2H), 2.89 (dq, J=8.6, 7.1 Hz, 1H), 2.02 (d, J=4.3 Hz, 2H), 1.70 (d, J=1.3 Hz, 3H), 1.59 (dd, J=7.0, 1.2 Hz, 3H), 1.56–1.48 (m, 4H), 1.15 (d, J=7.1 Hz, 3H), 1.07 (d, J=1.5 Hz, 9H); 13C NMR (176 MHz, CDCl3): δ [ppm]=211.3, 165.9, 140.9, 135.6, 134.1, 133.6, 129.8, 129.6, 128.5, 127.6, 125.1, 75.0, 70.4, 63.7, 60.4, 48.9, 39.3, 32.1, 26.9, 23.9, 21.1, 19.2, 16.8, 15.6, 14.2; HRMS (ESI+) calcd for C36H46O5SiNa+ [M+Na]+: 609.3007; found: 609.3007.

Ketone 31: Method A with chlorodicylohexylborane (8.70 mL, 8.70 mmol), DMEA (1.26 mL, 11.6 mmol) in Et2O (45 mL), ketone 16 (1.20 g, 5.82 mmol) in Et2O (45 mL) and aldehyde 30 (2.63 g, 7.00 mmol) in Et2O (3.5 mL). Work‐up MeOH (10 mL), buffer (pH 7, 10 mL), H2O2 (5 mL) and CH2Cl2 (3×50 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 31 (1.80 g, 3.12 mmol, 54 %, dr >20 : 1). R f=0.34 (SiO2, CH/EtOAc, 4 : 1); [α] 25.2° (c=0.31, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=8.13–8.08 (m, 2H), 7.71–7.66 (m, 4H), 7.63–7.59 (m, 1H), 7.50–7.38 (m, 8H), 5.46 (q, J=7.1 Hz, 1H), 3.77 (ddd, J=9.7, 7.0, 2.5 Hz, 1H), 3.67 (t, J=6.5 Hz, 2H), 2.88 (p, J=7.2 Hz, 1H), 1.59 (d, J=7.1 Hz, 3H), 1.57–1.55 (m, 2H), 1.52 (tq, J=7.9, 2.8, 2.3 Hz, 2H), 1.42–1.31 (m, 6H), 1.29 (d, J=7.2 Hz, 3H), 1.06 (s, 9H); 13C NMR (176 MHz, CDCl3): δ [ppm]=212.1, 165.9, 135.6, 134.2, 133.4, 129.8, 129.5, 129.4, 128.5, 63.9, 60.4, 48.2, 34.5, 32.5, 29.3, 26.9, 25.8, 25.5, 15.9, 14.6; HRMS (ESI+) calcd for C35H46O5SiNa+ [M+Na]+: 597.3307; found: 597.3007.

General method B: TBS protection, LiBH: To a stirred solution of β‐hydroxyketone (1.00 equiv) in CH2Cl2 at −78 °C was added 2,6‐lutidine (2.00 equiv) and TBS ⋅ OTf (1.50 equiv). The reaction was stirred for 1.5 h and quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

To a solution of protected alcohol (1.00 equiv) in THF at −78 °C was added LiBH4 (15.0 equiv) in one portion. After stirring 2 h at −78 °C, the mixture was stirred 3 days at room temperature. At 0 °C, water was added followed by careful addition of a saturated solution of NH4Cl. The mixture was poured to a mixture of water and Et2O (1 : 1). After separation of the organic layer, the aqueous layer was extracted with Et2O. The organic layers were combined, dried MgSO4 and evaporated in vacuo. The residue was purified by column chromatography.

To a solution of diol (1.00 equiv) in dioxane and water (2 : 1) at 0 °C was added NaIO4 (2.50 equiv) portionwise. The reaction mixture was vigorously stirred overnight then diluted with CH2Cl2, and the reaction was quenched with water. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The residue was purified by column chromatography.

Aldehyde 18: Method B with β‐hydroxyketone (3.23 g, 5.50 mmol), 2,6‐lutidine (1.26 mL,10.9 mmol), TBSOTf (1.88 mL, 8.17 mmol) in CH2Cl2 (120 mL). Work‐up NaHCO3 (80 mL) and CH2Cl2 (80 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1) gave TBS‐protected alcohol (3.64 g, 94 %). Protected alcohol (3.64 g, 5.19 mmol), LiBH4 (1.68 g, 77.1 mmol) in THF (120 mL). Work‐up H2O (40 mL), NH4Cl (5 mL) and Et2O/H2O (1 : 1, 100 mL). Chromatography (SiO2, CH/EtOAc, 4 : 1) gave the diol (3.01 g, 98 %, dr=4 : 1). Diol (3.01 g, 5.09 mmol), NaIO4 (2.68 g, 12.5 mmol) in dioxane /water (120 mL). Work‐up water (50 mL) and CH2Cl2 (3×100 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 18 (2.33 g 4.22 mmol, 83 %). R f=0.65 (SiO2, CH/EtOAc, 5 : 1); [α] =‐17.4° (c=0.39, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=δ 9.73 (d, J=2.9 Hz, 1H), 7.68–7.65 (m, 4H), 7.44–7.41 (m, 2H), 7.38 (ddt, J=8.1, 6.7, 1.1 Hz, 4H), 5.16 (dp, J=9.1, 1.3 Hz, 1H), 4.58–4.52 (m, 1H), 3.68 (t, J=6.0 Hz, 2H), 2.42–2.35 (m, 1H), 2.06–1.97 (m, 2H), 1.65 (d, J=1.4 Hz, 3H), 1.60–1.50 (m, 7H), 1.04 (s, 9H), 0.94 (d, J=7.0 Hz, 3H), 0.85 (d, J=2.7 Hz, 9H), −0.02 (s, 3H), −0.04 (s, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=204.7, 137.8, 135.5, 134.1, 129.5, 127.6, 126.4, 71.2, 63.7, 53.5, 39.2, 32.2, 26.6, 25.5, 23.9, 19.1, 17.9, 16.5, 10.3, −4.2, −5.4; HRMS (ESI+) calcd for C33H52O4Si2Na+ [M+Na]+: 575.3347; found: 575.3347.

Aldehyde 32: Method B with β‐hydroxyketone (888 mg, 1.54 mmol), 2,6‐lutidine (0.36 mL,3.08 mmol), TBSOTf (0.53 mL, 2.31 mmol) in CH2Cl2 (50 mL). Work‐up NaHCO3 (25 mL), CH2Cl2 (25 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1) gave TBS‐protected alcohol (996 mg, 85 %). Protected alcohol (885 mg, 1.33 mmol), LiBH4 (340 mg, 15.7 mmol) in THF (40 mL). Work‐up H2O (15 mL), NH4Cl (2 mL) and Et2O/H2O (1 : 1, 40 mL). Chromatography (SiO2, CH/EtOAc, 4 : 1) gave the diol (750 mg, quant., dr=4 : 1). Diol (750 mg, 1.33 mmol), NaIO4 (683 mg, 3.20 mmol) in dioxane /water (30 mL). Work‐up water (20 mL) and CH2Cl2 (3×20 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 32 (583 mg, 1.07 mmol, 85 %). R f=0.66 (SiO2, CH/EtOAc, 5 : 1); = −22.6° (c=0.35, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=9.74 (d, J=2.3 Hz, 1H), 7.70–7.63 (m, 4H), 7.47–7.33 (m, 6H), 3.91 (q, J=5.5 Hz, 1H), 3.65 (t, J=6.4 Hz, 2H), 2.49 (ddd, J=7.1, 4.9, 2.3 Hz, 1H), 1.59–1.50 (m, 6H), 1.44 (ddd, J=15.4, 9.5, 4.2 Hz, 1H), 1.38–1.23 (m, 7H), 1.07 (d, J=7.0 Hz, 3H), 1.04 (s, 9H), 0.88 (s, 9H), 0.06 (d, J=4.0 Hz, 6H); 13C NMR (125 MHz, CDCl3): δ [ppm]=205.2, 135.6, 134.2, 129.5, 127.6, 73.5, 63.9, 51.1, 34.8, 32.5, 29.5, 26.9, 25.8, 24.8, 19.2, 18.1, 10.5, −4.2, −4.7; HRMS (ESI+) calcd for C34H56O3Si2K+ [M+K]+: 579.3087; found: 579.3090.

General method C: Still‐Gennari olefination. To a solution of [18]crown‐6 (2.30 equiv,) and phosphonate 19 (1.40 equiv) in THF at −78 °C was added KHMDS (1.30 equiv) over 10 min. The reaction was stirred for 30 min then the aldehyde (1.00 equiv) in THF was added dropwise and the reaction was stirred for another 2 h at −78 °C. The reaction was quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4, evaporated in vacuo and purified by column chromatography.

Ester 20: Method C with [18]crown‐6 (2.52 g, 9.55 mmol), 19 (1.93 g, 5.82 mmol), KHMDS (10.8 mL, 8.40 mmol) in THF (100 mL), aldehyde 18 (2.30 g, 4.15 mmol) in THF (4 mL). Work‐up NaHCO3 (100 mL) and CH2Cl2 (240 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 20 (2.38 g, 3.82 mmol, 92 %, dr > 20 : 1). R f=0.56 (SiO2, CH/EtOAc, 10 : 1); [α] =+9.1° (c=0.32, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=7.75–7.66 (m, 4H), 7.49–7.38 (m, 6H), 5.84 (dq, J=10.1, 1.4 Hz, 1H), 5.09 (dq, J=9.1, 1.3 Hz, 1H), 4.21 (dd, J=9.0, 5.9 Hz, 1H), 3.72 (s, 3H), 3.68 (t, J=6.0 Hz, 2H), 3.26–3.15 (m, 1H), 1.98 (t, J=7.3 Hz, 2H), 1.90 (d, J=1.4 Hz, 3H), 1.60 (d, J=1.3 Hz, 3H), 1.58–1.48 (m, 4H), 1.07 (s, 9H), 0.96 (dd, J=6.9, 2.6 Hz, 3H), 0.88 (s, 9H), −0.02 (s, 3H), −0.04 (s, 3H); 13C NMR (125 MHz, CDCl3): δ [ppm]=146.0, 135.8, 135.6, 134.1, 129.5, 127.6, 127.3, 126.4, 73.0, 63.7, 51.1, 40.8, 39.3, 32.2, 26.9, 25.8, 24.0, 21.0, 19.2, 18.1, 16.6, 16.1, −4.1, −4.9; HRMS (ESI+) calcd for C37H58O4Si2Na+ [M+Na]+: 645.3766; found: 645.3766.

Ester 22: Method C with [18]crown‐6 (2.13 g, 8.14 mmol), 19 (1.64 g, 4.96 mmol), KHMDS (9.2 mL, 4.6 mmol) in THF (100 mL), aldehyde 21 (2.12 g, 3.54 mmol) in THF (4 mL). Work‐up NaHCO3 (100 mL) and CH2Cl2 (240 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 22 (2.17 g, 3.27 mmol, 93 %, dr > 20 : 1). R f =0.56 (SiO2, CH/EtOAc, 10 : 1); [α] =+28.1° (c=0.31, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=7.68–7.66 (m, 4H), 7.42–7.36 (m, 6H), 6.41–6.38 (m, 1H), 5.09 (ddt, J=11.8, 9.0, 1.4 Hz, 2H), 4.10 (dd, J=9.0, 5.9 Hz, 1H), 3.70 (s, 3H), 3.66 (t, J=6.1 Hz, 2H), 2.40 (dq, J=10.0, 6.5 Hz, 1H), 1.97–1.93 (m, 5H), 1.77–1.74 (m, 3H), 1.58 (d, J=1.3 Hz, 3H), 1.55–1.43 (m, 4H), 1.04 (d, J=1.5 Hz, 9H), 0.86–0.83 (m, 13H), −0.01 (s, 3H), −0.04 (s, 3H); 13C NMR (125 MHz, CDCl3): δ [ppm]=169.8, 135.6, 134.1, 133.5, 131.4, 129.5, 127.9, 127.6, 127.3, 73.1, 63.7, 51.4, 40.6, 39.3, 62.2, 26.9, 25.8, 24.0, 22.2, 21.2, 19.2, 18.2, 16.6, 16.0, −4.3, −4.9; HRMS (ESI+) calcd for C40H62O4Si2Na+ [M+Na]+: 686.4079; found: 686.4097.

Ester 33: Method C with [18]crown‐6 (674 mg, 2.55 mmol), 19 (516 mg, 1.55 mmol), KHMDS (2.9 mL, 1.44 mmol) in THF (20 mL), aldehyde 32 (594 mg, 1.11 mmol) in THF (2 mL). Work‐up NaHCO3 (30 mL) and CH2Cl2 (100 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 33 (610 mg, 1.00 mmol, 91 %, dr > 20 : 1). R f=0.66 (SiO2, CH/EtOAc, 5 : 1); [α] =+5.2° (c=0.33, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=7.69–7.68 (m, 4H), 7.45–7.42 (m, 2H), 7.41–7.38 (m, 4H), 5.94 (dq, J=10.1, 1.4 Hz, 1H), 3.73 (s, 3H), 3.66 (t, J=6.5 Hz, 2H), 3.55 (td, J=6.1, 3.6 Hz, 1H), 3.30 (dqd, J=10.4, 6.8, 3.5 Hz, 1H), 1.93 (d, J=1.4 Hz, 3H), 1.40–1.18 (m, 10H), 1.06 (s, 9H), 1.00 (d, J=6.8 Hz, 3H), 0.92 (s, 9H), 0.07 (s, 3H), 0.06 (s, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=168.5, 144.8, 135.6, 134.2, 129.5, 127.6, 126.6, 75.7, 64.0, 51.2, 38.0, 35.1, 32.6, 29.6, 26.9, 26.0, 25.8, 25.5, 21.1, 19.2, 18.2, 17.0, −4.2, −4.5; HRMS (ESI+) calcd for C36H58O4Si2Na+ [M+Na]+: 633.3766, found : 633.3763.

Ester 35: Method C with [18]crown‐6 (536 mg, 2.05 mmol), 19 (416 mg, 1.25 mmol), KHMDS (2.3 mL, 1.16 mmol) in THF (20 mL), aldehyde 34 (520 mg, 0.96 mmol) in THF (2 mL). Work‐up NaHCO3 (30 mL) and CH2Cl2 (100 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 35 (510 mg, .078 mmol, 87 %, dr > 20 : 1). R f=0.55 (SiO2, CH/EtOAc, 20 : 1); [α] =+0.9° (c=0.22, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=7.67 (dt, J=6.7, 1.5 Hz, 4H), 7.43–7.36 (m, 6H), 6.38–6.36 (m, 1H), 5.16 (dp, J=9.9, 1.6 Hz, 1H), 3.70 (s, 3H), 3.65 (t, J=6.5 Hz, 2H), 3.44 (dt, J=7.0, 4.3 Hz, 1H), 2.44 (dqd, J=13.7, 6.8, 3.9 Hz, 1H), 1.97 (d, J=1.6 Hz, 3H), 1.79–1.77 (m, 3H), 1.57–1.54 (m, 2H), 1.35–1.29 (m, 4H), 1.28–1.19 (m, 3H), 1.17–1.12 (m, 1H), 1.04 (s, 9H), 0.90–0.88 (m, 12H), 0.01 (d, J=3.0 Hz, 6H); 13C NMR (176 MHz, CDCl3): δ [ppm]=169.4, 136.1, 134.2, 131.9, 129.5, 128.4, 127.6, 75.8, 64.0, 51.4, 35.8, 33.6, 32.6, 29.7, 26.9, 26.0, 25.9, 22.5, 21.1, 19.2, 18.1, 15.9, −4.3, −4.5; HRMS (ESI+) calcd for C39H62O4Si2Na+ [M+Na]+: 637.4079; found: 673.4079.

General method D: Red‐Ox sequence from ester to aldehyde. To a solution of ester (1.00 equiv) in CH2Cl2 at −78 °C was added DIBAL‐H (3.00 equiv) dropwise. The mixture was stirred for 1 h and warmed up to 0 °C for 45 min. CH2Cl2 was added followed by H2O2, a 3 M aqueous solution of NaOH and H2O (1 : 1 : 2.5). After stirring 15 min at room temperature, MgSO4 was added and the mixture was stirred an additional 15 min. After filtration, the solvent was removed in vacuo.

D1= With MnO. The crude product was directly diluted in CH2Cl2 and MnO2 (20.0 equiv) was added. The reaction was stirred overnight at room temperature. The solution was filtered through celite and the solvent was evaporated in vacuo. The residue was purified by column chromatography.

Aldehyde 21: Method D1 with ester 20 (2.38 g, 3.82 mmol), DIBAL‐H (11.4 mL, 11.4 mmol), in CH2Cl2 (50 mL). Work‐up CH2Cl2 (50 mL), H2O2 (0.45 mL), 3 M NaOH (0.45 ml), H2O (1.1 mL). Crude product and MnO2 (6.64 g, 76.4 mmol) in CH2Cl2 (40 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 21 (2.12 g, 3.54 mmol, 94 % over 2 steps). R f=0.56 (SiO2, CH/EtOAc, 10 : 1); [α] =+11.8° (c=0.51, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=10.04 (d, J=0.5 Hz, 1H), 7.69–7.63 (m, 4H), 7.45–7.34 (m, 6H), 6.34 (dq, J=10.9, 1.3 Hz, 1H), 5.06 (dq, J=9.3, 1.4 Hz, 1H), 4.19–4.13 (m, 1H), 3.66 (t, J=6.0 Hz, 2H), 3.17 (dp, J=10.7, 6.7 Hz, 1H), 2.02–1.95 (m, 2H), 1.77 (d, J=1.4 Hz, 3H), 1.62 (d, J=1.3 Hz, 3H), 1.54–1.46 (m, 4H), 1.04 (s, 9H), 1.00 (d, J=6.7 Hz, 3H), 0.82 (d, J=2.6 Hz, 9H), −0.02 (s, 3H), −0.04 (s, 3H); 13C NMR (125 MHz, CDCl3): δ [ppm]=192.1, 152.6, 136.0, 135.9, 135.5, 134.1, 129.5, 127.6, 127.0, 73.0, 63.6, 39.3, 38.4, 32.2, 26.9, 25.7, 23.9, 19.2, 18.1, 17.2, 16.8, 16.6, −4.1, −4.9; HRMS (ESI+) calcd for C36H56O3Si2Na+ [M+Na]+: 615.3660; found: 615.3664.

Aldehyde 23: Method D1 with ester 22 (2.17 g, 3.27 mmol), DIBAL‐H (9.81 mL, 9.81 mmol), in CH2Cl2 (50 mL). Work‐up CH2Cl2 (50 mL), H2O2 (0.40 mL), 3 M NaOH (0.40 ml), H2O (1.0 mL). Crude product and MnO2 (5.69 g, 65.4 mmol) in CH2Cl2 (40 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 23 (1.96 g, 3.09 mmol, 95 % over 2 steps). R f=0.61 (SiO2, CH/EtOAc, 20 : 1); [α] =+11.3° (c=0.77, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=9.90 (s, 1H), 7.70–7.64 (m, 5H), 7.44–7.35 (m, 7H), 6.92 (dd, J=2.3, 1.2 Hz, 1H), 5.40 (dq, J=10.2, 1.4 Hz, 1H), 5.03 (dq, J=9.0, 1.3 Hz, 1H), 4.09 (dd, J=8.9, 6.2 Hz, 1H), 3.66 (t, J=6.1 Hz, 2H), 2.35–2.27 (m, 1H), 1.98–1.94 (m, 2H), 1.88 (q, J=2.1, 1.6 Hz, 2H), 1.81 (d, J=1.4 Hz, 2H), 1.56 (d, J=1.3 Hz, 2H), 1.53–1.45 (m, 3H), 1.05–1.04 (m, 9H), 0.87–0.83 (m, 12H) −0.01 (s, 3H), −0.04 (s, 3H); 13C NMR (125 MHz, CDCl3): δ [ppm]=193.4, 147.0, 136.2, 135.8, 135.6, 134.1, 129.5, 127.6, 127.4, 73.2, 63.7, 40.9, 39.3, 32.2, 26.9, 25.8, 25.0, 24.0, 19.2, 18.1, 16.6, 16.3, 15.9, −4.2, −4.9; HRMS (ESI+) calcd for C39H60O3Si2Na+ [M+Na]+: 655.3973; found: 655.3973.

Aldehyde 25: Method D1 with ester 24 (582 mg, 0.84 mmol), DIBAL‐H (2.50 mL, 2.50 mmol), in CH2Cl2 (10 mL). Work‐up CH2Cl2 (20 mL), H2O2 (0.1 mL), 3 M NaOH (0.1 ml), H2O (0.2 mL). Crude product and MnO2 (1.46 g, 16.8 mmol) in CH2Cl2 (6 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 25 (540 mg, 0.82 mmol, 98 % over 2 steps). R f=0.50 (SiO2, CH/EtOAc, 10 : 1); [α] =+17.0° (c=0.37, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=9.61 (d, J=7.9 Hz, 1H), 7.70–7.68 (m, 5H), 7.53 (dd, J=15.7, 0.8 Hz, 1H), 7.45–7.43 (m, 2H), 7.41–7.38 (m, 5H), 6.29 (dd, J=2.2, 1.2 Hz, 1H), 6.18 (ddt, J=15.7, 7.8, 0.7 Hz, 1H), 5.32 (dt, J=10.2, 1.5 Hz, 1H), 5.08–5.05 (m, 1H), 4.10 (dd, J=8.9, 6.2 Hz, 1H), 3.68 (t, J=6.1 Hz, 2H), 2.29 (dp, J=10.3, 6.8 Hz, 1H), 1.97 (t, J=7.4 Hz, 2H), 1.95 (d, J=1.3 Hz, 3H), 1.86–1.85 (m, 3H), 1.59 (dd, J=1.3, 0.7 Hz, 3H), 1.57–1.54 (m, 2H), 1.49 (qd, J=7.1, 3.4 Hz, 2H), 1.06 (d, J=0.6 Hz, 10H), 0.87 (d, J=0.6 Hz, 12H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=194.0, 150.8, 139.9, 135.8, 135.5, 134.8, 134.2, 131.7, 131.2, 129.5, 128.9, 127.6, 127.3, 73.1, 63.8, 40.7, 39.3, 32.2, 26.6, 25.6, 24.1, 24.0, 19.4, 19.1, 18.0, 16.4, 15.6, −4.5, −5.2; HRMS (ESI+) calcd for C41H62O3Si2Na+ [M+Na]+: 681.4130; found: 681.4130.

D2= With DMP. DMP (1.20 eq) was added to a solution of crude alcohol in DCM at 0 °C. The mixture was stirred for 1 to 3 h at room temperature and quenched with a saturated solution of NaHCO3/Na2S3O3 (2 : 1). After separation of the organic layer, the aqueous layer was extracted with DCM. The combined organic layers were dried over MgSO4, evaporated in vacuo and purified by column chromatography.

Aldehyde 34: Method D2 with ester 33 (620 mg, 1.01 mmol), DIBAL‐H (3.00 mL, 3.00 mmol), in CH2Cl2 (10 mL). Work‐up CH2Cl2 (20 mL), H2O2 (0.12 mL), 3 M NaOH (0.12 ml), H2O (0.30 mL). Crude product and DMP (517 mg, 1.21 mmol) in CH2Cl2 (10 mL). Work‐up NaHCO3/Na2S3O3 (30 mL) and DCM (60 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 34 (525 mg, 0.96 mmol, 90 % over 2 steps). R f=0.52 (SiO2, CH/EtOAc, 20 : 1); [α] =+8.8° (c=0.26, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=10.08 (d, J=0.5 Hz, 1H), 7.68–7.65 (m, 4H), 7.43–7.40 (m, 2H), 7.39–7.36 (m, 4H), 6.45 (dq, J=10.8, 1.3 Hz, 1H), 3.64 (t, J=6.4 Hz, 2H), 3.55 (td, J=5.7, 4.6 Hz, 1H), 3.33–3.27 (m, 1H), 1.79 (d, J=1.3 Hz, 3H), 1.56–1.53 (m, 4H), 1.46 (ddt, J=13.7, 10.4, 5.0 Hz, 1H), 1.40–1.31 (m, 3H), 1.30–1.21 (m, 4H), 1.06 (d, J=6.8 Hz, 3H), 1.04 (s, 9H), 0.88 (s, 9H); 13C NMR (176 MHz, CDCl3): δ [ppm]=191.6, 152.1, 135.6, 134.2, 129.5, 127.6, 75.6, 63.9, 35.6, 34.9, 32.5, 29.6, 26.9, 25.9, 25.8, 24.8, 19.2, 18.6, 18.1, 16.7, −4.2, −4.4; HRMS (ESI+) calcd for C35H56O3Si2Na+ [M+Na]+: 603.3660; found: 603.3663.

Aldehyde 36: Method D2 with ester 35 (507 mg, 0.78 mmol), DIBAL‐H (2.33 mL, 2.33 mmol), in CH2Cl2 (12 mL). Work‐up CH2Cl2 (15 mL), H2O2 (0.10 mL), 3 M NaOH (0.10 ml), H2O (0.20 mL). Crude product and DMP (396 mg, 0.93 mmol) in CH2Cl2 (10 mL). Work‐up NaHCO3/Na2S3O3 (15 mL) and DCM (45 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 36 (416 mg, 0.67 mmol, 86 % over 2 steps). R f=0.52 (SiO2, CH/EtOAc, 20 : 1); [α] =+6.2° (c=0.26, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=9.89 (s, 1H), 7.68–7.65 (m, 4H), 7.42–7.36 (m, 6H), 6.94 (dd, J=2.5, 1.3 Hz, 1H), 5.44 (dt, J=10.3, 1.5 Hz, 1H), 3.65 (t, J=6.5 Hz, 2H), 3.46–3.38 (m, 1H), 2.40 (ddd, J=10.5, 6.9, 3.9 Hz, 1H), 1.90 (dd, J=1.4, 0.8 Hz, 3H), 1.83 (d, J=1.5 Hz, 3H), 1.38–1.20 (m, 9H), 1.04 (s, 9H), 0.91 (d, J=6.8 Hz, 3H), 0.88 (s, 9H), −0.00 (d, J=7.1 Hz, 6H); 13C NMR (176 MHz, CDCl3): δ [ppm]=193.1, 146.8, 136.5, 135.6, 135.3, 134.2, 129.8, 129.5, 127.6, 75.8, 64.0, 38.5, 33.9, 32.6, 29.6, 25.9, 25.6, 25.1, 19.2, 18.1, 16.2, 15.8, −4.3, −4.5; HRMS (ESI+) calcd for C38H60O3Si2Na+ [M+Na]+: 643.3973; found: 643.3973.

Aldehyde 38: Method D2 with ester 37 (120 mg, 0.18 mmol), DIBAL‐H (.053 mL, 0.53 mmol), in CH2Cl2 (7 mL). Work‐up CH2Cl2 (15 mL), H2O2 (0.08 mL), 3 M NaOH (0.08 ml), H2O (0.15 mL). Crude product and DMP (90 mg, 0.21 mmol) in CH2Cl2 (4 mL). Work‐up NaHCO3/Na2S3O3 (12 mL) and DCM (30 mL) Chromatography (SiO2, CH/EtOAc, 20 : 1) gave 38 (416 mg, 0.67 mmol, 90 % over 2 steps). R f=0.52 (SiO2, CH/EtOAc, 20 : 1); [α] =+3.3° (c=0.24, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=9.61 (dd, J=7.8, 5.5 Hz, 1H), 7.69–7.64 (m, 4H), 7.50–7.43 (m, 1H), 7.42–7.34 (m, 6H), 6.27 (s, 1H), 6.16 (dd, J=15.7, 7.8 Hz, 1H), 5.35 (dt, J=10.2, 1.5 Hz, 1H), 3.64 (t, J=6.4 Hz, 2H), 3.40 (dd, J=6.4, 4.0 Hz, 1H), 2.34 (ddd, J=10.5, 6.9, 3.8 Hz, 1H), 1.94 (d, J=1.4 Hz, 2H), 1.87–1.81 (m, 2H), 1.26 (dt, J=21.0, 11.2 Hz, 8H), 1.04 (s, 9H), 0.91 (d, J=6.8 Hz, 3H), 0.88 (d, J=2.7 Hz, 9H), 0.04—0.06 (m, 6H); 13C NMR (176 MHz, CDCl3): δ [ppm]=194.2, 150.7, 139.9, 135.6, 134.2, 134.0, 132.0, 131.5, 129.5, 129.1, 127.6, 75.9, 64.0, 38.5, 33.7, 32.6, 29.6, 26.9, 25.9, 24.5, 19.6, 19.2, 18.1, 15.8, −4.3, −4.6; HRMS (ESI+) calcd for C40H62O3Si2Na+ [M+Na]+: 669.4130; found: 669.4130.

General method E: HWE olefination. To a solution of trimethyl phosphonoacetate 13 c (1.50 equiv) and DMPU (1.50 equiv) in THF at 0 °C was added nBuLi (1.40 equiv). The mixture was stirred for 30 min then the aldehyde (1.00 equiv) in THF was added dropwise. After stirring for 2 h at 0 °C, the reaction was stirred overnight at room temperature. The reaction was quenched with buffer pH 7 and H2O at 0 °C. After separation of the organic layer, the aqueous layer was extracted with Et2O. The organic layers were combined, dried over MgSO4, evaporated in vacuo and purified by column chromatography.

Ester 24: Method E with 13 c (0.75 mL, 4.64 mmol), DMPU (0.56 mL, 4.64 mmol, nBuLi (2.7 mL, 4.33 mmol) and aldehyde 23 (1.96 g, 3.09 mmol) in THF (80 mL). Work‐up at pH 7 (50 mL) and Et2O (300 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 24 (2.03 g, 2.94 mmol, 95 %). R f=0.53 (SiO2, CH/EtOAc, 20 : 1); [α] =+39.3° (c=0.41, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=7.68–7.62 (m, 5H), 7.41–7.35 (m, 6H), 6.17 (td, J=1.5, 0.8 Hz, 1H), 5.86 (dd, J=15.8, 0.7 Hz, 1H), 5.23–5.17 (m, 1H), 5.05 (dq, J=9.2, 1.3 Hz, 1H), 4.08 (dd, J=9.0, 5.8 Hz, 1H), 3.74 (s, 3H), 3.66 (td, J=6.0, 2.5 Hz, 3H), 2.30–2.22 (m, 1H), 1.98–1.93 (m, 2H), 1.89 (d, J=1.4 Hz, 3H), 1.80 (dd, J=1.4, 0.7 Hz, 3H), 1.57 (d, J=1.3 Hz, 3H), 1.54–1.46 (m, 5H), 1.04 (d, J=2.0 Hz, 11H), 0.88–0.86 (m, 3H), 0.86–0.82 (m, 9H), −0.06 (s, 5H); 13C NMR (125 MHz, CDCl3): δ [ppm]=167.8, 143.3, 138.3, 135.5, 134.5, 134.1, 131.3, 131.2, 129.5, 127.6, 127.1, 117.8, 72.9, 63.7, 51.4, 40.8, 39.3, 62.2, 26.8, 25.8, 24.5, 24.0, 19.8, 19.2, 18.1, 16.6, 15.5, −4.3, −4.9; HRMS (ESI+) calcd for C42H64O4Si2Na+ [M+Na]+: 711.4235, found : 711.4238.

Ester 37: Method E with 13 c (0.16 mL, 1.00 mmol), DMPU (0.12 mL, 1.00 mmol, nBuLi (0.58 mL, 0.94 mmol) and aldehyde 36 (416 mg, 0.67 mmol) in THF (15 mL). Work‐up at pH 7 (15 mL), Et2O (60 mL). Chromatography (SiO2, CH/EtOAc, 9 : 1) gave 37 (416 mg, 0.67 mmol, 89 %). R f=0.52 (SiO2, CH/EtOAc, 20 : 1); [α] =+40.4° (c=0.26, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=7.68–7.65 (m, 4H), 7.61 (dd, J=15.8, 0.7 Hz, 1H), 7.43–7.36 (m, 6H), 6.15 (d, J=1.9 Hz, 1H), 5.87 (dd, J=15.8, 0.7 Hz, 1H), 5.29 (dt, J=10.3, 1.4 Hz, 1H), 3.74 (s, 3H), 3.64 (t, J=6.5 Hz, 2H), 3.39 (ddd, J=6.9, 4.8, 3.5 Hz, 1H), 2.32 (ddd, J=10.4, 6.9, 3.7 Hz, 1H), 1.89 (d, J=1.4 Hz, 3H), 1.81 (dd, J=1.4, 0.7 Hz, 3H), 1.59–1.54 (m, 2H), 1.38–1.18 (m, 9H), 1.04 (d, J=1.7 Hz, 9H), 0.92 (d, J=6.8 Hz, 3H), 0.87 (s, 9H), −0.02 (s, 3H), −0.03 (s, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=167.7, 142.2, 138.0, 135.6, 134.2, 133.3, 131.6, 129.5, 127.6, 118.0, 75.9, 64.0, 51.5, 38.5, 33.5, 32.6, 29.6, 26.9, 26.0, 25.9, 24.6, 19.6, 19.2, 18.1, 15.5, −4.4, −4.6; HRMS (ESI+) calcd for C41H64O4Si2Na+ [M+Na]+: 699.4235; found: 699.4235.

General method F: Ipc boron mediated aldol reaction and TBS protection. (−)‐Ipc2BH (1.00 equiv) was dissolved in anhydrous hexane and cooled down at 0 °C. Triflic acid (1.00 equiv) was added dropwise and the mixture was stirred at room temperature until no Ipc2BH crystals were seen to afford a stock solution of triflate of 1.9 M. The stock solution (1.30 equiv) was diluted in CH2Cl2 and cooled down to −78 °C. DIEA (3.00 equiv) was added dropwise followed by diethylketone 26 (1.40 equiv). The reaction mixture was stirred for 3 h at this temperature. Then the aldehyde (1.00 equiv) in CH2Cl2 was added, the reaction was stirred for 1 h at −78 °C and stored overnight at −20 °C. Buffer (pH 7), MeOH and H2O2 (2 : 2 : 1) were added, and the solution was stirred for 1 h at room temperature. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4, evaporated in vacuo and purified by column chromatography.

To a stirred solution of β‐hydroxyketone (1.00 equiv) in CH2Cl2 at −78 °C was added 2,6‐lutidine (2.00 equiv) and TBSOTf (1.50 equiv). The reaction was stirred for 1.5 h and quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

Ketone 27: Method F with TfOH (336 μL, 3.81 mmol), Ipc2BH (1.09 g, 3.81 mmol) in hexane (0.88 mL). Triflate stock solution (0.55 mL, 1.05 mmol), DIEA (360 μL, 2.10 mmol), diethylketone 26 (100 μL, 0.98 mmol) and aldehyde 25 (460 mg, 0.70 mmol) in CH2Cl2 (8 mL). Work‐up at pH 7 buffer (4 mL), MeOH (4 mL), H2O2 (2 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1) gave the corresponding β‐hydroxyketone (310 mg, 0.42 mmol, 61 %, dr = 10:1). The β‐hydroxyketone (370 mg, 0.50 mmol), 2,6‐lutidine (0.11 mL, 1.00 mmol) and TBS ⋅ OTf (0.17 mL, 0.75 mmol) in CH2Cl2 (8 mL). Work‐up NaHCO3 (10 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1) gave 27 (383 mg, 0.44 mmol, 90 %). R f=0.18 (SiO2, CH/EtOAc, 10 : 1); [α] =+56.2° (c=0.34, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=7.68–7.66 (m, 4H), 7.43–7.41 (m, 2H), 7.38 (ddt, J=8.2, 6.7, 1.2 Hz, 4H), 6.44–6.39 (m, 1H), 5.93–5.91 (m, 1H), 5.60–5.54 (m, 1H), 5.11 (dq, J=9.7, 1.5 Hz, 1H), 5.08 (dp, J=9.0, 1.2 Hz, 1H), 4.35 (ddd, J=6.9, 5.8, 1.2 Hz, 0H), 4.31 (ddd, J=7.7, 5.9, 1.0 Hz, 1H), 4.14–4.10 (m, 1H), 3.68 (t, J=6.2 Hz, 2H), 2.70 (qd, J=6.9, 5.7 Hz, 1H), 2.53–2.38 (m, 2H), 2.37–2.31 (m, 1H), 2.00–1.96 (m, 2H), 1.84–1.81 (m, 3H), 1.78–1.76 (m, 3H), 1.58 (d, J=1.4 Hz, 2H), 1.57–1.54 (m, 2H), 1.50 (ddd, J=8.5, 6.7, 4.7 Hz, 2H), 1.04–1.02 (m, 12H), 0.95 (t, J=7.2 Hz, 3H), 0.87 (s, 9H), 0.85 (d, J=4.4 Hz, 12H), 0.03 (s, 3H), −0.01 (d, J=4.4 Hz, 6H), −0.03—0.04 (m, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=212.6, 135.5, 135.4, 134.2, 132.7, 132.1, 131.9, 130.6, 130.4, 129.7, 129.5, 127.6, 127.2, 76.0, 72.9, 63.8, 52.9, 40.5, 39.3, 36.5, 32.2, 26.6, 25.7, 25.6, 24.5, 24.0, 20.1, 19.1, 18.0, 19.7, 16.4, 15.4, 12.1, 7.2, −4.3, −4.6, −5.1, −5.2; HRMS (ESI+) calcd for C52H88O4Si3Na+ [M+Na]+: 881.5726; found: 881.5726.

Ketone 39: Method F with TfOH (167 μL, 1.93 mmol), Ipc2BH (545 mg, 1.93 mmol) in hexane (0.44 mL). Triflate solution (0.22 mL, 0.76 mmol), DIEA (145 μL, 0.83 mmol), diethylketone 26 (41 μL, 0.39 mmol) and aldehyde 38 (180 mg, 0.28 mmol) in CH2Cl2 (4 mL).Work‐up buffer pH 7, (2 mL), MeOH (2 mL), H2O2 (1 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1) gave the corresponding β‐hydroxyketone (132 mg, 0.18 mmol, 64 %, dr = 10:1). The β‐hydroxyketone (145 mg, 0.20 mmol), 2,6‐lutidine (46 μL, 0.40 mmol) and TBS ⋅ OTf (68 μL, 0.30 mmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (5 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave 39 (153 mg, 0.18 mmol, 90 %). R f=0.54 (SiO2, CH/EtOAc, 10 : 1); [α] =+23.0° (c=0.31, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=7.73–7.67 (m, 4H), 7.51–7.36 (m, 6H), 6.39 (d, J=15.7 Hz, 1H), 5.89 (s, 1H), 5.59 (dd, J=15.8, 7.4 Hz, 1H), 5.17 (d, J=9.6 Hz, 1H), 4.34 (t, J=6.8 Hz, 1H), 3.67 (t, J=6.5 Hz, 2H), 3.42 (s, 1H), 2.72 (p, J=6.8 Hz, 1H), 2.49 (dq, J=10.4, 7.2 Hz, 3H), 1.84 (d, J=1.4 Hz, 3H), 1.58 (d, J=7.4 Hz, 2H), 1.40–1.23 (m, 8H), 1.10–1.05 (m, 12H), 1.01 (t, J=7.2 Hz, 4H), 0.89 (dd, J=2.8, 1.3 Hz, 21H), −0.00—0.03 (m, 12H); 13C NMR (176 MHz, CDCl3): δ [ppm]=213.3, 135.6, 134.2, 131.8, 130.7, 130.3, 129.6, 129.5, 127.6, 75.9, 75.8, 64.0, 53.0, 38.7, 36.6, 33.0, 32.6, 29.7, 26.9, 26.3, 26.0, 25.9, 24.6, 20.2, 19.2, 18.1, 15.3, 12.5, 7.2, −4.0, −4.4, −4.5, −4.9; HRMS (ESI+) calcd for C51H86O4Si3Na+ [M+Na]+: 869.5726; found: 869.5727.

General method G: TDBPS deprotection and TES protection. To a solution of TBAF (1.00 equiv) in THF at 0 °C was added AcOH (1.00 equiv) resulting in a 41.5 mM stock solution. To the neat alcohol (1.00 equiv) was added the TBAF stock solution at 0 °C (1.10 equiv). The reaction was stirred for 1 h at this temperature then 30 h at room temperature. The reaction was diluted with Et2O and quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with Et2O. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

To a solution of alcohol (1.00 equiv) in CH2Cl2 at −78 °C was added 2,6‐lutidine (2.00 equiv) followed by TES ⋅ OTf (1.50 equiv). The reaction mixture was stirred 1 h and quenched with water at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The combined organic layers were dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

Ketone 28: Method G with TBAF (830 μL,0.84 mmol), AcOH (48 μL, 0.84 mmol) in THF (10.6 mL).Neat alcohol 27 (340 mg, 0.40 mmol) and stock solution (10.6 mL, 0.44 mmol). Work‐up NaHCO3 (10 mL) and Et2O (10 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave the unprotected alcohol (180 mg, 0.29 mmol, 73 %). Unprotected alcohol (102 mg, 0.16 mmol), 2,6‐lutidine (38 μL, 0.33 mmol), TES ⋅ OTf (56 μL, 0.25 mmol) in CH2Cl2 (4 mL). Work‐up H2O (4 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave 28 (108 mg, 0.15 mmol, 90 %). R f=0.59 (SiO2, CH/EtOAc, 10 : 1); [α] =+61.0° (c=0.29, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.41 (d, J=15.8 Hz, 1H), 5.92 (s, 1H), 5.59–5.55 (m, 1H), 5.12–5.07 (m, 2H), 4.32–4.30 (m, 1H), 4.12 (dd, J=8.9, 5.9 Hz, 1H), 3.60 (t, J=6.2 Hz, 4H), 2.72–2.68 (m, 1H), 2.53–2.39 (m, 2H), 2.33 (ddd, J=16.9, 10.1, 5.0 Hz, 1H), 1.98 (t, J=7.1 Hz, 2H), 1.83 (d, J=1.1 Hz, 3H), 1.77 (s, 3H), 1.58 (s, 3H), 1.50–1.43 (m, 4H), 1.03 (d, J=6.9 Hz, 3H), 0.96 (dt, J=14.5, 5.2 Hz, 12H), 0.89 (s, 3H), 0.87 (d, J=3.0 Hz, 9H), 0.85–0.84 (m, 9H), 0.58 (dt, J=8.0, 5.3 Hz, 6H), 0.03 (s, 3H), −0.01 (s, 6H), −0.03 (s, 6H); 13C NMR (700 MHz, CD2Cl2): δ [ppm]=212.8, 135.5, 132.7, 132.1, 131.9, 130.6, 130.4, 129.7, 127.1, 76.0, 72.9, 62.6, 52.9, 40.5, 39.4, 36.4, 32.6, 25.6, 25.6, 24.5, 24.1, 20.1, 18.0, 17.9, 16.4, 15.4, 13.8, 12.1, 7.2, 6.6, 4.4, −4.3, −4.6, −5.2; HRMS (ESI+) calcd for C42H86O4Si3N [M+NH4]+: 752.5859; found: 752.5859.

Ketone 40: Method G with TBAF (830 μL,0.84 mmol), AcOH (48 μL, 0.84 mmol in THF (10.6 mL). Neat protected alcohol 39 (340 mg, 0.40 mmol) and stock solution (10.6 mL, 0.44 mmol). Work‐up NaHCO3 (10 mL) and Et2O (10 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave the unprotected alcohol (180 mg, 0.29 mmol, 73 %). Unprotected alcohol (127 mg, 0.32 mmol), 2,6‐lutidine (48 μL, 0.42 mmol), TES ⋅ OTf (78 μL, 0.31 mmol) in CH2Cl2 (4 mL). Work‐up H2O (4 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave 40 (140 mg, 0.19 mmol, 90 %). R f=0.52 (SiO2, CH/EtOAc, 10 : 1); [α] =+26.1° (c=0.62, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.39 (dt, J=15.7, 0.9 Hz, 1H), 5.89 (d, J=1.7 Hz, 1H), 5.60–5.56 (m, 1H), 5.19–5.16 (m, 1H), 4.33 (ddd, J=7.2, 5.9, 1.0 Hz, 1H), 3.58 (td, J=6.7, 1.8 Hz, 2H), 3.43 (td, J=6.5, 6.0, 3.8 Hz, 1H), 2.69 (qd, J=6.9, 5.7 Hz, 1H), 2.54–2.37 (m, 3H), 1.84–1.81 (m, 2H), 1.78–1.74 (m, 3H), 1.51–1.47 (m, 2H), 1.36–1.15 (m, 8H), 1.04 (d, J=6.9 Hz, 3H), 0.95 (td, J=7.6, 4.5 Hz, 12H), 0.89–0.88 (m, 3H), 0.88 (d, J=2.7 Hz, 9H), 0.87 (s, 9H), 0.59 (q, J=8.0 Hz, 6H), 0.05 (s, 3H), −0.01 (s, 6H), −0.04 (s, 3H); 13C NMR (700 MHz, CD2Cl2): δ [ppm]=212.6, 132.4, 132.4, 131.7, 130.8, 130.2, 129.4, 75.9, 75.8, 62.8, 53.8, 53.7, 53.6, 53.6, 53.5, 53.4, 53.3, 53.3, 53.1, 52.9, 38.6, 36.4, 33.1, 33.0, 29.7, 26.2, 25.9, 25.7, 25.7, 25.6, 25.6, 25.6, 24.6, 19.9, 18.0, 17.9, 15.1, 12.1, 7.2, 6.5, 4.4, −4.3, −4.7, −4.8, −5.2; HRMS (ESI+) calcd for C41H82O4Si3Na+ [M+Na]+: 745.5413; found: 745.5410.

General method H: Aldol condensation sequence. LiTMP stock solution: To a solution of TMP (4.00 equiv) in THF at −78 °C was added nBuLi (4.00 equiv). The yellow solution was stirred for 15 min at this temperature and 15 min at 0 °C.

The ketone (1.00 equiv) was diluted in THF and cooled down at −78 °C. LiTMP (2.00 equiv) was added dropwise. The mixture was stirred for 30 min at −78 °C and warmed up to −50 °C for 20 min. The enolate solution was cooled down to −78 °C and the aldehyde (1.50 equiv) was added dropwise. After 2 h, the reaction mixture was diluted with CH2Cl2 and quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4, evaporated in vacuo and purified by column chromatography.

The mixture of diastereoisomers was directly diluted in THF, DMAP (5.00 equiv) and Ac2O (4.00 equiv) were added at 0 °C. After 30 min, buffer pH 7 was added. After separation of the organic layer, the aqueous layer was extracted with Et2O. The organic layers were combined, dried over MgSO4, evaporated under vacuum and purified by column chromatography.

The protected alcohol was diluted in THF and DBU (35.0 equiv) was added at room temperature. After one night, the reaction was quenched with buffer (pH 7). After separation of the organic layer, the aqueous layer was extracted with EtOAc. The organic layers were combined, dried over MgSO4, evaporated under vacuum and purified by column chromatography.

Ketone 43 a: Method H with TMP (32 μL, 0.18 mmol), nBuLi (0.12 mL, 0.18 mmol) in THF (0.8 mL). Ketone 27 (40 mg, 47 μmol), LiTMP (0.50 mL, 94 μmol) in THF (1.5 mL) and aldehyde 41 (10 mg, 70 μmol) in THF (0.2 mL). Work‐up NaHCO3 (2 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1 to 10 : 1) gave the aldol product (39 mg, 39 μmol, 83 %). Directly used with DMAP (24 mg, 0.19 mmol) and Ac2O (15 μL, 0.16 mmol) in THF (2 mL). Work‐up buffer (pH 7, 3 mL) and EtOAc (9 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave protected alcohol (35 mg, 33 μmol, 86 %). Directly used with DBU (175 μL, 1.29 mmol) in THF (2 mL). Work‐up buffer (pH 7, 2 mL) and EtOAc (9 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1) gave 43 a (31 mg, 32 μmol, 94 %, 67 % over 3 steps). R f=0.48 (SiO2, CH/EtOAc, 10 : 1). [α] =+24.7° (c=0.58, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=7.73–7.69 (m, 4H), 7.48–7.39 (m, 7H), 6.62–6.57 (m, 1H), 6.39 (dt, J=15.8, 0.8 Hz, 1H), 5.95 (s, 1H), 5.60–5.54 (m, 1H), 5.13 (dddd, J=10.3, 9.1, 2.8, 1.4 Hz, 2H), 4.33–4.24 (m, 1H), 4.16 (ddd, J=9.0, 5.9, 1.5 Hz, 1H), 4.09 (td, J=6.6, 5.0 Hz, 2H), 3.72 (t, J=6.0 Hz, 2H), 3.48–3.37 (m, 1H), 2.46–2.33 (m, 1H), 2.34–2.25 (m, 2H), 2.05 (d, J=2.0 Hz, 3H), 2.02 (t, J=7.2 Hz, 2H), 1.82 (d, J=1.3 Hz, 2H), 1.80 (d, J=0.6 Hz, 3H), 1.72 (q, J=0.9 Hz, 3H), 1.71–1.66 (m, 2H), 1.62 (d, J=1.4 Hz, 3H), 1.57 (s, 15H), 1.11 (dd, J=6.8, 2.0 Hz, 3H), 1.08 (s, 8H), 0.94–0.89 (m, 11H), 0.89–0.88 (m, 9H), 0.06 (s, 3H), 0.03 (s, 3H), 0.02 (s, 3H), 0.01 (s, 3H). 13C NMR (176 MHz, CD2Cl2): δ [ppm]=203.6, 170.8, 141.3, 137.9, 135.5, 135.4, 134.2, 132.8, 132.2, 132.0, 131.4, 130.1, 129.5, 129.3, 127.6, 127.2, 76.8, 72.9, 64.0, 63.8, 46.4, 40.6, 39.3, 32.2, 28.6, 28.4, 26.6, 25.6, 25.1, 24.6, 24.0, 20.7, 20.1, 19.6, 18.0, 16.4, 15.5, 14.0, 11.3, −4.2, −4.6, −5.1, −5.2. HRMS (ESI+) calcd for C59H96O6Si3Na+ [M+Na]+: 1007.6407; found: 1007.6407.

Ketone 43 b: Method H with TMP (120 μL, 0.70 mmol), nBuLi (0.28 mL, 0.70 mmol) in THF (2.0 mL). Ketone 39 (150 mg, 176 μmol), LiTMP stock solution (1.20 mL, 0.35 mmol) in THF (3.0 mL) and aldehyde 41 (38 mg, 265 μmol) in THF (0.5 mL). Work‐up NaHCO3 (4 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1 to 10 : 1) gave the aldol product (148 mg, 149 μmol, 85 %). Directly used with DMAP (91 mg, 0.75 mmol) and Ac2O (56 μL, 0.60 mmol) in THF (5 mL). Work‐up buffer (pH 7, 10 mL) and EtOAc (30 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1) gave protected alcohol (135 mg, 130 μmol, 87 %). Directly used with DBU (0.68 mL, 4.57 mmol) in THF (8 mL). Work‐up buffer (pH 7, 10 mL) and EtOAc (30 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1) gave 43 b (105 mg, 108 μmol, 83 %, 61 % over 3 steps). R f=0.48 (SiO2, CH/EtOAc, 10 : 1); [α] =+10.9° (c=0.35, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=7.66 (dt, J=6.8, 1.5 Hz, 4H), 7.42 (ddt, J=8.4, 6.5, 1.5 Hz, 2H), 7.40–7.36 (m, 4H), 6.59–6.53 (m, 1H), 6.33 (dt, J=15.8, 0.8 Hz, 1H), 5.91–5.86 (m, 1H), 5.59–5.53 (m, 1H), 5.19–5.16 (m, 1H), 4.28–4.25 (m, 1H), 4.05 (q, J=6.5 Hz, 2H), 3.66 (td, J=6.5, 2.2 Hz, 2H), 3.44 (td, J=6.6, 5.8, 3.5 Hz, 1H), 3.39 (q, J=6.9 Hz, 1H), 2.44–2.37 (m, 1H), 2.30–2.23 (m, 2H), 2.04–1.99 (m, 3H), 1.79–1.77 (m, 3H), 1.76 (t, J=1.1 Hz, 3H), 1.70 (p, J=1.3 Hz, 2H), 1.68–1.64 (m, 2H), 1.59–1.55 (m, 2H), 1.37–1.21 (m, 8H), 1.10–1.06 (m, 2H), 1.04 (s, 9H), 0.91–0.89 (m, 3H), 0.88 (d, J=2.7 Hz, 9H), 0.87 (s, 8H), −0.00—0.03 (m, 12H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=203.6, 170.8, 141.3, 137.8, 135.5, 134.2, 132.5, 132.4, 131.6, 131.5, 129.9, 129.5, 129.0, 127.5, 76.6, 75.9, 64.0, 63.9, 46.4, 38.6, 33.2, 32.6, 29.6, 28.6, 28.4, 26.6, 26.2, 25.9, 25.7, 25.6, 25.1, 24.6, 20.7, 20.0, 19.1, 18.0, 15.2, 14.0, 11.4, −4.3, −4.7, −4.8, −5.1; HRMS (ESI+) calcd for C58H100O6Si3N+ [M+NH4]+: 990.6853; found: 990.6853.

Ketone 44 a: Method H with TMP (94 μL, 0.28 mmol), nBuLi (0.11 mL, 0.28 mmol) in THF (2.0 mL). Ketone 28 (104 mg, 140 μmol), LiTMP stock solution (1.1 mL, 0.28 mmol) in THF (3.0 mL) and aldehyde 42 (45 mg, 211 μmol) in THF (0.5 mL). Work‐up NaHCO3 (4 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1 to 20 : 1) gave the aldol product (117 mg, 123 μmol, 88 %). Directly used with DMAP (75 mg, 0.62 mmol) and Ac2O (47 μL, 0.49 mmol) in THF (4 mL). Work‐up buffer (pH 7, 5 mL) and EtOAc (20 mL). Chromatography (SiO2, CH/EtOAc, 30 : 1) gave protected alcohol (111 mg, 112 μmol, 91 %). Directly used with DBU (0.58 mL, 3.92 mmol) in THF (6 mL). Work‐up buffer (pH 7, 10 mL) and EtOAc (30 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1) gave 44 a (84 mg, 90 μmol, 80 %, 64 % over 3 steps). R f=0.67 (SiO2, CH/EtOAc, 10 : 1); [α] =‐14.7° (c=0.32, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=7.03–6.98 (m, 1H), 6.53–6.47 (m, 1H), 6.37–6.33 (d, 1H), 6.17–6.11 (m, 1H), 5.90 (dd, J=11.8, 6.9 Hz, 1H), 5.56–5.52 (m, 1H), 5.11–5.06 (m, 1H), 4.26–4.22 (m, 1H), 4.14–4.10 (m, 1H), 3.72–3.70 (m, 2H), 3.60 (t, J=6.2 Hz, 2H), 3.42 (dd, J=13.8, 6.9 Hz, 1H), 2.41 (q, J=6.5 Hz, 2H), 2.32 (ddd, J=15.6, 9.5, 4.6 Hz, 1H), 2.00–1.96 (m, 2H), 1.78 (s, 3H), 1.78–1.76 (m, 6H), 1.58 (d, J=1.1 Hz, 3H), 1.49–1.44 (m, 4H), 1.09 (d, J=6.8 Hz, 1H), 0.96–0.94 (m, 9H), 0.90–0.89 (m, 12H), 0.87–0.86 (m, 9H), 0.85 (d, J=1.2 Hz, 9H), 0.60–0.57 (m, 6H), 0.06 (d, J=2.2 Hz, 6H), 0.02 (d, J=1.4 Hz, 3H), −0.01—0.02 (m, 3H), −0.02—0.03 (m, 3H), −0.04 (d, J=1.4 Hz, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=203.6, 147.7, 139.8, 138.0, 135.6, 135.2, 132.6, 132.3, 131.9, 131.4, 130.1, 129.2, 128.4, 127.2, 76.8, 73.0, 62.6, 62.2, 46.3, 40.6, 39.6, 36.9, 32.7, 25.6, 24.6, 24.3, 20.3, 18.2, 17.7, 16.5, 15.5, 14.2, 11.5, 6.5, 4.3, −4.2, −4.6, −5.1, −5.2, −5.6; HRMS (ESI+) calcd for C53H102O5Si4Na+ [M+Na]+: 953 : 6697; found: 953.6697.

Ketone 44 b: Method H with TMP (134 μL, 0.40 mmol), nBuLi (0.30 mL, 0.40 mmol) in THF (2.0 mL). Ketone 40 (145 mg, 200 μmol), LiTMP stock solution (1.3 mL, 0.40 mmol) in THF (3.0 mL) and aldehyde 42 (65 mg, 300 μmol) in THF (0.5 mL). Work‐up NaHCO3 (4 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1 to 50 : 1) gave the aldol product (148 mg, 157 μmol, 78 %). Directly used with DMAP (96 mg, 0.78 mmol) and Ac2O (59 μL, 0.63 mmol) in THF (5 mL). Work‐up buffer (pH 7, 5 mL) and EtOAc (20 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave protected alcohol (130 mg, 133 μmol, 85 %). Directly used with DBU (0.69 mL, 4.64 mmol) in THF (5 mL). Work‐up buffer (pH 7, 10 mL) and EtOAc (30 mL). Chromatography (SiO2, CH/EtOAc, 100 : 1) gave 44 b (108 mg, 117 μmol, 88 %, 58 % over 3 steps). R f=0.67 (SiO2, CH/EtOAc, 10 : 1); [α] =‐29.6° (c=0.23, CHCl3); 1H NMR (500 MHz, CD2Cl2): δ [ppm]=7.07–6.99 (m, 1H), 6.54 (dd, J=15.3, 10.7 Hz, 1H), 6.36 (d, J=15.8 Hz, 1H), 6.17 (dt, J=14.3, 6.9 Hz, 1H), 5.91 (s, 1H), 5.63–5.54 (m, 1H), 5.21 (dt, J=9.6, 1.6 Hz, 1H), 4.35–4.27 (m, 1H), 3.75 (t, J=6.4 Hz, 2H), 3.62 (td, J=6.6, 1.3 Hz, 2H), 3.51–3.37 (m, 2H), 2.45 (q, J=6.6 Hz, 3H), 1.83 (d, J=1.1 Hz, 3H), 1.82–1.76 (m, 6H), 1.51 (dd, J=10.5, 4.0 Hz, 2H), 1.33 (dd, J=11.4, 7.3 Hz, 8H), 1.15–1.10 (m, 3H), 1.02–0.96 (m, 9H), 0.93 (s, 12H), 0.91 (t, J=2.4 Hz, 17H), 0.62 (qd, J=7.9, 0.8 Hz, 6H), 0.09 (s, 6H), 0.06 (s, 3H), 0.05 (s, 3H), −0.01 (s, 3H), −0.04 (s, 3H); 13C NMR (125 MHz, CD2Cl2): δ [ppm]=203.6, 139.7, 138.1, 134.9, 132.5, 132.4, 131.6, 129.8, 128.9, 128.3, 76.5, 75.9, 62.8, 62.8, 62.2, 53.8, 53.6, 53.5, 53.4, 53.2, 53.1, 52.9, 46.3, 38.6, 36.8, 33.1, 32.9, 30.0, 29.7, 26.2, 25.9, 25.7, 25.6, 25.6, 25.4, 24.6, 19.9, 18.1, 18.0, 15.2, 14.1, 11.5, 6.5, 4.3, −4.3, −4.7, −4.8, −4.8, −5.1, −5.6, −5.7; HRMS (ESI+) calcd for C52H102O5Si4Na+ [M+Na]+: 941.6679; found: 941.6679.

General method I: Reduction and methylation at the C18 position. To a solution of ketone (1.00 equiv) in MeOH and THF at 0 °C was added NaBH4 (4.00 equiv) and the solution was warmed up to room temperature. After 3 h, the reaction was diluted with EtOAc and quenched carefully with a saturated solution of NH4Cl at 0 °C. After separation of the organic layer, the aqueous layer was extracted with EtOAc. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

To a solution of alcohol (1.00 equiv) in CH2Cl2 at 0 °C was added proton sponge (5.50 equiv) followed by Me3OBF4 (5.00 equiv). The reaction was stirred for 3 to 5 h at 0 °C. After this time, a saturated solution of NaHCO3 was added at 0 °C. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4, evaporated in vacuo and purified by column chromatography.

Methyl ether 45 a: Method I with ketone 43 a (65 mg, 66 μmol) and NaBH4 (5 mg, 132 μmol) in MeOH (3 mL) and THF (1 mL). Work‐up with NH4Cl (4 mL) and EtOAc (35 mL). Chromatography (SiO2, CH/EtOAc, 60 : 1 to 30 : 1) gave the alcohol (44 mg, 45 μmol, 67 %, dr=10 : 1). The alcohol (42 mg, 42 μmol) was used with proton sponge (46 mg, 0.23 mmol) and Me3OBF4 (31 mg, 0.21 mmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 60 : 1) gave 45 a (37 mg, 37 μmol, 89 %, 60 % over 2 steps). R f=0.46 (SiO2, CH/EtOAc, 10 : 1); [α] =+29.8° (c=0.48, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=7.71–7.70 (m, 4H), 7.47–7.44 (m, 2H), 7.43–7.41 (m, 4H), 6.46 (dt, J=15.9, 0.9 Hz, 1H), 5.75 (ddd, J=15.9, 6.9, 0.7 Hz, 1H), 5.35–5.33 (m, 1H), 5.12 (dddq, J=9.7, 4.3, 3.0, 1.4 Hz, 2H), 4.72 (dt, J=7.0, 1.5 Hz, 1H), 4.16 (dd, J=9.0, 5.8 Hz, 1H), 4.07 (t, J=6.7 Hz, 2H), 3.71 (t, J=6.2 Hz, 2H), 3.34 (d, J=10.0 Hz, 1H), 3.13 (s, 3H), 2.44–2.38 (m, 1H), 2.18–2.09 (m, 2H), 2.04 (s, 4H), 2.03–1.99 (m, 2H), 1.88 (d, J=1.4 Hz, 3H), 1.82 (dt, J=2.8, 1.4 Hz, 2H), 1.70–1.64 (m, 3H), 1.62–1.57 (m, 7H), 1.50–1.44 (m, 6H), 1.07 (s, 9H), 0.95 (s, 9H), 0.93–0.92 (m, 3H), 0.88 (d, J=2.7 Hz, 10H), 0.67 (dd, J=6.9, 2.4 Hz, 3H), 0.08 (d, J=4.3 Hz, 3H), 0.02 (s, 6H), 0.01 (s, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=170.9, 135.5, 135.4, 134.2, 134.0, 133.5, 132.6, 132.5, 132.2, 130.2, 129.5, 129.1, 127.7, 127.6, 127.1, 88.3, 72.8, 71.8, 64.3, 63.8, 55.1, 42.4, 40.5, 32.2, 28.3, 27.1, 16.6, 25.9, 25.7, 25.6, 24.5, 24.0, 20.7, 20.2, 19.1, 18.1, 18.0, 16.3, 15.1, 9.8, 8.9, −4.1, −4.6, −5.2, −5.4; HRMS (ESI+) calcd for C60H100O6Si3Na [M+Na]+: 1023.6720; found: 1023.6720.

Methyl ether 45 b: Method I with ketone 43 b (105 mg, 108 μmol) and NaBH4 (8 mg, 216 μmol) in MeOH (5 mL) and THF (2 mL). Work‐up with NH4Cl (8 mL) and EtOAc (40 mL). Chromatography (SiO2, CH/EtOAc, 60 : 1 to 30 : 1) gave the alcohol (73 mg, 75 μmol, 70 %, dr=10 : 1). Directly used with proton sponge (88 mg, 0.41 mmol) and Me3OBF4 (55 mg, 0.37 mmol) in CH2Cl2 (4 mL). Work‐up NaHCO3 (5 mL) and CH2Cl2 (30 mL). Chromatography (SiO2, CH/EtOAc, 60 : 1) gave 45 b (60 mg, 61 μmol, 82 %, 57 % over 2 steps). R f=0.44 (SiO2, CH/EtOAc, 10 : 1); [α] =+4.5° (c=0.33, CHCl3); 1H NMR (500 MHz, CD2Cl2): δ [ppm]=7.68–7.65 (m, 4H), 7.43–7.35 (m, 6H), 6.39 (d, J=15.9 Hz, 1H), 5.80 (s, 1H), 5.69 (dd, J=15.9, 6.8 Hz, 1H), 5.29 (t, J=6.6 Hz, 1H), 5.13–5.10 (m, 1H), 4.68 (d, J=6.8 Hz, 1H), 4.07 (t, J=6.6 Hz, 2H), 3.65 (t, J=6.5 Hz, 2H), 3.41–3.37 (m, 1H), 3.30 (d, J=10.0 Hz, 1H), 3.11 (s, 3H), 2.42–2.38 (m, 1H), 2.09 (dt, J=13.9, 6.9 Hz, 2H), 2.05 (s, 3H), 1.83 (d, J=1.2 Hz, 3H), 1.78 (s, 3H), 1.64 (dt, J=14.7, 6.6 Hz, 2H), 1.59–1.55 (m, 2H), 1.47–1.42 (m, 5H), 1.36–1.20 (m, 8H) 1.04 (s, 9H), 0.92–0.90 (s, 9H), 0.89–0.87 (m, 3H), 0.87–0.86 (m, 9H), 0.64–0.61 (d, J=6.9 Hz 2H), 0.03 (d, J=2.5 Hz, 3H), −0.01‐(‐0.02) (s, 6H), −0.03 (s, 3H); 13C NMR (125 MHz, CD2Cl2): δ [ppm]=171.2, 135.6, 134.3, 134.2, 133.5, 132.8, 132.6, 131.7, 130.1, 129.5, 128.9, 127.6, 127.5, 88.4, 75.8, 71.6, 64.4, 64.0, 55.4, 42.4, 38.6, 32.7, 32.6, 29.7, 28.3, 27.2, 26.9, 26.3, 25.9, 24.9, 21.0, 20.4, 19.3, 18.2, 18.1, 14.8, 10.0, 9.1, −3.8, −4.5, −4.6, −5.1; HRMS (ESI+) calcd for C59H104O6Si3N+ [M+NH4]+: 1006.7166; found: 1006.7166.

Methyl ether 46 a: Method I with ketone 44 a (84 mg, 90 μmol) and NaBH4 (14 mg, 360 μmol) in MeOH (3 mL) and THF (1 mL). Work‐up with NH4Cl (4 mL) and EtOAc (35 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the alcohol (67 mg, 73 μmol, 86 %, dr=8 : 1). Directly used with proton sponge (86 mg, 0.40 mmol) and Me3OBF4 (54 mg, 0.36 mmol) in CH2Cl2 (4 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 80 : 1) gave 46 a (50 mg, 53 μmol, 72 %, 62 % over 2 steps). R f=0.69 (SiO2, CH/EtOAc, 10 : 1); [α] =+15.6° (c=0.41, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=6.45–6.41 (m, 1H), 6.38–6.32 (m, 1H), 5.92 (t, J=8.1 Hz, 2H), 5.86 (s, 1H), 5.73–5.62 (m, 2H), 5.08 (ddd, J=8.3, 5.1, 1.3 Hz, 2H), 4.69 (d, J=7.0 Hz, 1H), 4.15–4.10 (m, 2H), 3.66 (t, J=6.6 Hz, 2H), 3.60 (t, J=6.1 Hz, 2H), 3.34 (d, J=9.9 Hz, 1H), 3.10 (s, 3H), 2.39–2.29 (m, 3H), 1.98 (t, J=7.2 Hz, 2H), 1.85–1.84 (m, 3H), 1.79 (s, 3H), 1.57 (d, J=1.4 Hz, 6H), 1.50–1.43 (m, 4H), 0.95 (dd, J=10.3, 5.5 Hz, 9H), 0.92 (s, 9H), 0.89 (s, 12H), 0.86–0.86 (m, 3H), 0.64–0.62 (m, 3H), 0.59 (q, J=8.0 Hz, 6H), 0.05 (d, J=1.3 Hz, 3H), 0.05 (s, 6H), −0.01 (s, 3H), −0.01 (s, 3H), −0.04 (s, 3H). 13C NMR (176 MHz, CDCl3): δ [ppm]=135.4, 134.2, 133.9, 132.5, 132.1, 130.7, 129.6, 129.1, 127.7, 126.9, 88.1, 72.8, 71.7, 62.8, 62.5, 55.3, 42.6, 40.4, 39.3, 36.5, 32.5, 25.7, 25.6, 25.6, 24.5, 24.1, 20.1, 18.1, 18.0, 17.9, 16.4, 15.1, 10.3, 8.7, 6.5, 4.3, −4.1, −4.7, −5.3, −5.4, −5.6; HRMS (ESI+) calcd for C54H110O5Si3N+ [M+NH4]+: 964.7456; found: 964.7456.

Methyl ether 46 b: Method I with ketone 44 b (78 mg, 85 μmol) and NaBH4 (13 mg, 340 μmol) in MeOH (4 mL) and THF (1 mL). Work‐up with NH4Cl (4 mL) and EtOAc (35 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the alcohol (67 mg, 73 μmol, 86 %, dr=10 : 1). Directly used with proton sponge (86 mg, 0.40 mmol) and Me3OBF4 (54 mg, 0.36 mmol) in CH2Cl2 (4 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 80 : 1) gave 46 b (57 mg, 61 μmol, 84 %, 72 % over 2 steps). R f=0.69 (SiO2, CH/EtOAc, 10 : 1); [α] =‐7.2° (c=0.25, CHCl3); 1H NMR (700 MHz, CDCl3): δ [ppm]=6.41–6.37 (m, 1H), 6.33 (ddt, J=15.0, 10.6, 1.3 Hz, 1H), 5.92–5.88 (m, 1H), 5.80 (s, 1H), 5.71–5.64 (m, 2H), 5.13–5.10 (m, 1H), 4.69 (dt, J=6.9, 1.6 Hz, 1H), 3.67 (t, J=6.7 Hz, 2H), 3.59 (t, J=6.8 Hz, 3H), 3.40 (td, J=8.7, 7.9, 4.7 Hz, 1H), 3.34 (d, J=10.0 Hz, 1H), 3.13 (d, J=9.8 Hz, 3H), 2.40 (tt, J=10.8, 6.5 Hz, 1H), 2.36–2.32 (m, 2H), 1.83 (d, J=1.4 Hz, 3H), 1.78 (q, J=1.8, 1.1 Hz, 3H), 1.60 (s, 1H), 1.59–1.57 (m, 3H), 1.53–1.49 (m, 3H), 1.34–1.27 (m, 7H), 1.15 (tt, J=9.8, 5.8 Hz, 1H), 0.96 (t, J=7.9 Hz, 12H), 0.92 (d, J=6.4 Hz, 9H), 0.89 (d, J=2.9 Hz, 13H), 0.87–0.86 (m, 9H), 0.63 (d, J=6.9 Hz, 2H), 0.60 (t, J=8.0 Hz, 6H), 0.05 (s, 6H), 0.04 (s, 3H), −0.01 (s, 3H), –0.02 (s, 3H), −0.03 (s, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=134.2, 134.2, 132.8, 132.6, 131.7, 130.6, 129.7, 129.0, 127.9, 127.5, 88.3, 77.2, 77.2, 77.0, 76.8, 75.8, 71.6, 63.0, 62.9, 55.6, 42.7, 38.7, 36.6, 33.0, 32.7, 29.7, 29.7, 26.3, 26.0, 26.0, 26.0, 26.0, 25.9, 25.9, 24.9, 20.4, 18.4, 18.2, 18.1, 14.8, 10.5, 9.0, 6.8, 4.5, −3.8, −4.5, −4.6, −5.1, −5.2, −5.2; HRMS (ESI+) calcd for C53H106O5Si4Na+ [M+Na]+: 934.7117; found: 934.7117.

General method J: Deprotection at the C1 position.

J1 = TBDPS group. To a solution of TBAF (1.00 equiv) in THF at 0 °C was added AcOH (1.00 equiv) resulting in a 41.5 mM solution stock solution. To the neat TBDPS‐protected alcohol (1.00 equiv) was added the stock solution at 0 °C (1.10 equiv). The reaction was stirred for 1 h at this temperature and 44 h at room temperature. The reaction was diluted with Et2O and quenched with a saturated solution of NaHCO3 at 0 °C. After separation of the organic layer, the aqueous layer was extracted with Et2O. The organic layers were combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

Alcohol 47 a: Method J1 with TBAF (415 μL, 0.42 mmol) and AcOH (24 μL, 0.42 mmol) in THF (9.6 mL). Alcohol 45 a (40 mg, 40 μmol) and TBAF stock solution (1.0 mL, 44 μmol). Work‐up NaHCO3 (2 mL) and Et2O (20 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 47 a (27 mg, 36 μmol, 88 %). R f=0.16 (SiO2, CH/EtOAc, 10 : 1); [α] =+34.8° (c=0.33, CHCl3, 20 °C); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.46–6.40 (m, 1H), 5.86 (s, 1H), 5.71 (dddd, J=16.0, 7.0, 3.6, 0.7 Hz, 1H), 5.31–5.28 (m, 1H), 5.14–5.05 (m, 2H), 4.71–4.65 (m, 1H), 4.14–4.09 (m, 1H), 4.03 (t, J=6.7 Hz, 2H), 3.62–3.57 (m, 2H), 3.30 (d, J=10.0 Hz, 1H), 3.10 (d, J=2.0 Hz, 3H), 2.36 (dqd, J=12.6, 6.7, 6.3, 3.6 Hz, 1H), 2.09 (dp, J=18.4, 7.3 Hz, 2H), 2.00 (d, J=3.3 Hz, 6H), 1.85–1.83 (m, 3H), 1.82–1.77 (m, 3H), 1.64–1.61 (m, 2H), 1.59–1.57 (m, 3H), 1.47–1.40 (m, 8H), 0.91 (s, 9H), 0.90–0.88 (m, 3H), 0.85 (s, 9H), 0.64 (dd, J=6.9, 4.4 Hz, 3H), 0.04 (s„ 3H), −0.01 (s, 6H), −0.03—0.05 (s, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=170.9, 135.2, 134.1, 133.5, 132.6, 132.5, 132.2, 130.2, 129.0, 127.7, 127.2, 88.3, 72.8, 71.8, 64.3, 62.6, 55.1, 42.4, 40.5, 39.3, 32.5, 28.3, 27.1, 25.9, 25.7, 25.6, 24.5, 23.9, 20.7, 20.2, 18.1, 18.0, 16.4, 15.2, 9.8, 8.9, −4.1, −4.7, −5.2, −5.4; HRMS (ESI+) calcd for C44H82O6Si2Na+ [M+Na]+: 785.5548; found: 785.5544.

Alcohol 47 b: Method J1 with TBAF (415 μL, 0.42 mmol) and AcOH (24 μL, 0.42 mmol) in THF (9.6 mL). Alcohol 45 b (58 mg, 59 μmol) and TBAF stock solution (1.6 mL, 65 μmol). Work‐up NaHCO3 (2 mL) and Et2O (20 mL). Chromatography (SiO2, CH/EtOAc, 20 : 1 to 10 : 1) gave 47 b (41 mg, 54 μmol, 92 %). R f=0.13 (SiO2, CH/EtOAc, 10 : 1); [α] =‐0.7° (c=0.22, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.46–6.40 (m, 1H), 5.86 (s, 1H), 5.71 (dddd, J=16.0, 7.0, 3.6, 0.7 Hz, 1H), 5.31–5.28 (m, 1H), 5.14–5.05 (m, 2H), 4.71–4.65 (m, 1H), 4.14–4.09 (m, 1H), 4.03 (t, J=6.7 Hz, 2H), 3.62–3.57 (m, 2H), 3.30 (d, J=10.0 Hz, 1H), 3.10 (d, J=2.0 Hz, 3H), 2.36 (dqd, J=12.6, 6.7, 6.3, 3.6 Hz, 1H), 2.09 (dp, J=18.4, 7.3 Hz, 2H), 2.00 (d, J=3.3 Hz, 6H), 1.85–1.83 (m, 3H), 1.82–1.77 (m, 3H), 1.64–1.61 (m, 2H), 1.59–1.57 (m, 3H), 1.44 (d, J=0.8 Hz, 9H), 0.91 (s, 9H), 0.90–0.88 (m, 3H), 0.85 (s, 9H), 0.64 (dd, J=6.9, 4.4 Hz, 3H), 0.05 (s, 3H), −0.01 (s, 6H), −0.04 (s, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=170.9, 134.4, 133.5, 132.8, 132.7, 131.6, 130.2, 128.9, 127.4, 88.3, 75.8, 71.7, 64.3, 62.8, 55.1, 42.5, 38.6, 32.9, 32.6, 29.6, 28.3, 27.1, 26.3, 25.9, 25.8, 25.7, 25.6, 25.4, 20.7, 20.0, 18.1, 17.9, 14.6, 9.7, 8.9, −4.1, −4.8, −4.9, −5.3; HRMS (ESI+) calcd for C43H82O6Si2Na+ [M+Na]+: 773.5542; found: 773.5542.

J2=TES group. To a solution of TES‐protected alcohol (1.00 equiv) in MeOH was added K2CO3 (30.0 equiv) at 0 °C. The solution was warmed up to room temperature and stirred overnight. The reaction was quenched with a saturated solution of NaHCO3 and diluted with EtOAc. After separation of the organic layer, the aqueous layer was extracted with EtOAc. The combined organic layers were dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

Alcohol 48 a: Method J2 with alcohol 46 a (48 mg, 51 μmol) and K2CO3 (210 mg, 1.53 μmol) in MeOH (7 mL). Work‐up NaHCO3 (10 mL) and EtOAc (40 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1) gave 48 a (35 mg, 42 μmol, 82 %). R f =0.22 (SiO2, CH/EtOAc, 10 : 1); [α] =+10.4° (c=0.25, CHCl3); 1H NMR (500 MHz, CDCl3): δ [ppm]=6.43 (d, J=15.9 Hz, 1H), 6.35 (dd, J=15.1, 10.8 Hz, 1H), 5.91 (d, J=11.2 Hz, 1H), 5.86 (s, 1H), 5.73–5.63 (m, 2H), 5.09 (dd, J=12.8, 5.3 Hz, 2H), 4.69 (d, J=7.0 Hz, 1H), 4.16–4.10 (m, 1H), 3.66 (t, J=6.6 Hz, 2H), 3.60 (t, J=11.8 Hz, 2H), 3.34 (d, J=9.9 Hz, 1H), 3.10 (s, 3H), 2.39–2.35 (m, 1H), 2.32 (dd, J=13.4, 6.7 Hz, 2H), 2.02–1.98 (m, 2H), 1.85 (d, J=1.2 Hz, 3H), 1.79 (s, 3H), 1.58 (dd, J=5.0, 3.8 Hz, 6H), 1.50–1.43 (m, 4H), 0.92 (s, 9H), 0.88 (d, J=1.9 Hz, 9H), 0.86 (d, J=3.2 Hz, 3H), 0.85 (s, 9H), 0.64–0.62 (m, 3H), 0.05 (d, J=1.5 Hz, 3H), 0.05 (s, 6H), −0.01 (s, 3H), −0.01 (s, 3H), −0.04 (s, 3H). 13C NMR (126 MHz, CDCl3): δ [ppm]=137.1, 136.2, 135.9, 134.5, 134.4, 134.1, 132.6, 131.6, 131.5, 131.0, 129.7, 129.1, 90.1, 74.7, 73.7, 64.7, 64.5, 57.2, 44.6, 42.3, 41.2, 38.4, 34.6, 27.7, 27.6, 27.6, 27.5, 26.4, 25.8, 22.1, 20.1, 18.3, 17.0, 12.3, 10.7, −2.2, −2.8, −3.3, −3.5, −3.7. HRMS (ESI+) calcd for C48H92O5Si3Na+ [M+Na]+: 855.6145; found: 855.6145.

Alcohol 48 b: Method J2 with alcohol 46 b (60 mg, 64 μmol) and K2CO3 (226 mg, 190 μmol) in MeOH (10 mL). Work‐up NaHCO3 (10 mL) and EtOAc (40 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1) gave 48 b (50 mg, 61 μmol, 94 %). R f=0.10 (SiO2, CH/EtOAc, 10 : 1); [α] =‐11.6° (c=0.32, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.40–6.36 (m, 1H), 6.36–6.32 (m, 1H), 5.94–5.90 (m, 1H), 5.81 (s, 1H), 5.74–5.65 (m, 2H), 5.16–5.12 (m, 1H), 4.70 (dt, J=6.9, 1.5 Hz, 1H), 3.66 (t, J=6.6 Hz, 2H), 3.58 (td, J=6.7, 5.3 Hz, 2H), 3.43 (ddd, J=9.8, 7.4, 4.3 Hz, 1H), 3.34 (d, J=9.9 Hz, 1H), 3.10 (s, 3H), 2.41 (dqd, J=10.6, 6.8, 3.7 Hz, 1H), 2.34–2.29 (m, 2H), 1.84 (d, J=1.4 Hz, 3H), 1.80–1.77 (m, 3H), 1.60–1.58 (m, 1H), 1.58–1.56 (m, 3H), 1.52–1.49 (m, 2H), 1.34–1.27 (m, 8H), 0.92 (d, J=6.5 Hz, 9H), 0.89 (d, J=4.0 Hz, 12H), 0.86 (s, 9H), 0.63–0.61 (m, 3H), 0.06 (s, 3H), 0.05 (s, 6H), −0.01 (s, 3H), −0.01 (s, 3H), −0.02 (s, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=134.3, 134.2, 132.8, 132.7, 131.6, 130.7, 129.6, 128.9, 127.8, 127.5, 88.2, 75.8, 71.7, 62.8, 62.8, 62.8, 55.3, 53.8, 53.7, 53.6, 53.6, 53.5, 53.4, 53.3, 53.1, 42.7, 38.6, 36.5, 32.9, 32.6, 29.7, 29.6, 26.3, 25.8, 25.8, 25.8, 25.7, 25.7, 25.7, 25.7, 25.7, 25.7, 24.5, 20.0, 18.2, 18.1, 18.0, 18.0, 14.5, 10.3, 8.8, −4.1, −4.8, −4.9, −5.3, −5.6, −5.6; HRMS (ESI+) calcd for C47H96O5Si3N+ [M+NH4]+: 838.6591; found: 838.6591.

General method K: C1 Oxidations to carboxylic acid, C23 deprotection, macrolactonization and global deprotection. To a solution of DMSO (10.0 equiv), sulfur trioxide pyridine complex (3.00 equiv) and DIEA (4.00 equiv) in CH2Cl2 at 0 °C was added alcohol (1.00 equiv) diluted in CH2Cl2. The solution was stirred at 0 °C for 1.5 h. After this time the reaction was quenched with aqueous saturated solution of NaHCO3 and diluted with CH2Cl2. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4 and evaporated in vacuo until 200 mbar. The crude product was then directly used in the next reaction.

The crude aldehyde was diluted in tert‐butanol and 2‐methylbut‐2‐ene (10 : 1) and cooled at 0 °C. A solution of NaClO2 (3.20 equiv), KH2PO4 (4.00 equiv) in H2O was added to the reaction mixture. The reaction was stirred for 1 h at room temperature. Saturated aqueous solution of NaCl was added and CH2Cl2. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The organic layers were combined, dried over MgSO4 and evaporated under vacuum.

K1:C23=Ac. The crude carboxylic acid was diluted in MeOH and K2CO3 was added (3.00 equiv). The reaction was stirred for 3 h at room temperature. The reaction was quenched with NaHCO3 and diluted with CH2Cl2. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The combined organic layers were washed with brine, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

K2:C23=TBS: To a solution of THF and pyridine at 0 °C was added HF‐pPyr (70 % HF) resulting in a stock solution. To a solution of carboxylic acid (1.00 equiv) in THF at 0 °C was added the HF‐pyr stock solution. The reaction was stirred for 6 h at 0 °C. The reaction was quenched with a saturated solution of NaHCO3 and diluted with CH2Cl2. After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The combined organic layers were washed with brine, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

MNBA (5.00 equiv), DMAP (7.00 equiv) and 4 Å MS were dried for 1 h under high vacuum before CH2Cl2 was added. The seco acid was diluted in CH2Cl2 and added to the solution over 20 h at room temperature. Two hours after completion of the addition, the reaction was quenched at 0 °C with buffer (pH 7). After separation of the organic layer, the aqueous layer was extracted with CH2Cl2. The combined organic layers were washed with brine, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

The macrolactone (1.00 equiv) was then diluted in THF and cooled down at 0 °C. Pyridine was added followed by HF‐pyr (70 % HF). After 1 day, the reaction was quenched at 0 °C with buffer (pH 7). After separation of the organic layer, the aqueous layer was extracted with EtOAc. The organic layers were washed with a saturated solution of NaHCO3, combined, dried over MgSO4 and evaporated in vacuo. The crude product was purified by column chromatography.

Analogue 5: Method K2 with DMSO (30 μL, 420 mmol), SO3‐pyr (20 mg, 126 μmol), DIEA (29 μL, 168 μmol) and alcohol 48 a (35 mg, 42 μmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Crude aldehyde diluted in tert‐butanol (2 mL) and 2‐methylbut‐2‐ene (0.2 mL) with NaClO2 (12 mg, 134 μmol) and KH2PO4 (23 mg, 168 μmol) in H2O (2 mL). Work‐up NaCl (4 mL) and CH2Cl2 (20 mL). Crude carboxylic acid and HF.‐pyr stock solution (0.34 mL, out of a solution of THF (1.3 mL), pyridine (0.75 mL), HF.‐pyr (0.25 mL, 75 % HF)) in THF (0.8 mL). Work‐up NaHCO3 (10 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 3 : 2) gave the corresponding seco acid (6.3 mg, 8.6 μmol, 32 % over 3 steps). Directly used with MNBA (15 mg, 43 μmol) and DMAP (7.3 mg, 60 μmol) in CH2Cl2 (4 mL). Seco acid diluted in CH2Cl2 (5 mL). Work‐up buffer (pH 7, 7 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the macrolactone (5.1 mg, 7.1 μmol, 83 %). Directly used with HF.‐pyr (0.3 mL) in THF (0.3 mL) and pyridine (0.3 mL). Work‐up buffer (pH 7, 5 mL) and EtOAC (20 mL). Chromatography (SiO2, CH/EtOAc, 5 : 1) gave 5 (1.2 mg, 3.4 μmol, 35 %, 6 % over 5 steps).

R f=0.45 (SiO2, CH/EtOAc, 3 : 1); [α] =‐33.4° (c=0.12, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.53 (d, J=16.0 Hz, 1H), 6.32 (dd, J=15.1, 10.9 Hz, 1H), 5.93 (d, J=10.7 Hz, 1H), 5.67 (dd, J=16.0, 4.8 Hz, 1H), 5.63 (s, 1H), 5.60–5.56 (m, 1H), 5.20–5.17 (m, 1H), 5.01 (dd, J=9.0, 1.1 Hz, 1H), 4.40 (d, J=4.5 Hz, 1H), 4.39–4.37 (m, 1H), 4.01–3.97 (m, 1H), 3.95 (d, J=9.4 Hz, 1H), 3.50 (d, J=9.0 Hz, 1H), 3.19 (s, 3H), 2.44 (dt, J=12.0, 3.9 Hz, 2H), 2.24 (ddd, J=9.9, 8.7, 5.4 Hz, 1H), 2.21–2.19 (m, 2H), 1.95 (td, J=9.8, 5.8 Hz, 2H), 1.89 (d, J=2.3 Hz, 3H), 1.82 (ddd, J=9.1, 7.3, 2.0 Hz, 1H), 1.77 (s, 3H), 1.71 (dd, J=6.3, 2.9 Hz, 2H), 1.67 (d, J=1.2 Hz, 3H), 1.63 (s, 3H), 0.71 (d, J=6.7 Hz, 3H), 0.57 (d, J=7.2 Hz, 3H); 13C NMR (176 MHz, CDCl3): δ [ppm]=173.3, 139.2, 134.6, 133.7, 132.6, 132.0, 131.1, 130.8, 128.9, 128.5, 128.0, 127.9, 126.8, 89.3, 72.9, 72.8, 62.6, 55.9, 40.9, 40.3, 39.2, 34.5, 32.7, 24.3, 23.8, 19.8, 17.1, 16.5, 11.8, 10.6; HRMS (ESI+) calcd for C30H46O5Na+ [M+Na]+: 509.3237; found: 509.3237.

Analogue 6: Method K1 with DMSO (25 μL, 354 mmol), SO3 .‐pyr (17 mg, 106 μmol), DIEA (25 μL, 141 μmol) and alcohol 47 a (27 mg, 35 μmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Crude aldehyde in tert‐butanol (2 mL) and 2‐methylbut‐2‐ene (0.2 mL) with NaClO2 (10 mg, 113 μmol) and KH2PO4 (19 mg, 141 μmol) in H2O (2 mL). Work‐up NaCl (4 mL) and CH2Cl2 (20 mL). Crude carboxylic acid with K2CO3 (15 mg, 106 μmol) in MeOH (2.5 mL). Work‐up NaHCO3 (5 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 3 : 2) gave the corresponding seco acid (5 mg, 7 μmol, 20 % over 3 steps). Directly used with MNBA (11 mg, 31 μmol) and DMAP (5.2 mg, 43 μmol) in CH2Cl2 (3 mL). Seco acid diluted in CH2Cl2 (4 mL). Work‐up buffer (pH 7, 3 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the macrolactone (4.3 mg, 6 μmol, 86 %). Directly used with HF‐.pyr (0.2 mL) in THF (0.3 mL) and pyridine (0.3 mL). Work‐up buffer (pH 7, 5 mL) and EtOAC (20 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 6 (1.2 mg, 2.5 μmol, 41 %, 7 % over 5 steps). R f=0.37 (SiO2, CH/EtOAc, 2 : 1); [α] =‐10.4° (c=0.1, CHCl3, 20 °C); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.51 (d, J=15.9 Hz, 1H), 5.71–5.67 (m, 1H), 5.66 (s, 1H), 5.38–5.35 (m, 1H), 5.18 (d, J=1.2 Hz, 1H), 4.99 (dd, J=9.1, 1.2 Hz, 1H), 4.32 (s, 1H), 4.09–4.05 (m, 1H), 3.99–3.93 (m, 2H), 3.43 (d, J=9.9 Hz, 1H), 3.17 (s, 3H), 2.27–2.18 (m, 5H), 2.07–2.03 (m, 2H), 2.01–1.97 (m, 2H), 1.91 (d, J=1.4 Hz, 3H), 1.77 (dd, J=1.4, 0.8 Hz, 3H), 1.72–1.68 (m, 2H), 1.65 (d, J=1.4 Hz, 3H), 1.59–1.55 (m, 2H), 1.51 (t, J=1.2 Hz, 3H), 1.45 (ddd, J=10.5, 4.4, 2.9 Hz, 2H), 0.73 (d, J=6.7 Hz, 3H), 0.60 (d, J=7.1 Hz, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=173.3, 138.4, 135.0, 132.9, 132.2, 131.9, 130.9, 130.6, 128.8, 18.7, 126.7, 90.1, 73.0, 71.7, 64.1, 55.4, 40.7, 40.4, 38.8, 34.1, 27.8, 26.6, 25.9, 24.3, 23.0, 19.7, 17.0, 16.7, 12.1, 9.8; HRMS (ESI+) calcd for C30H48O5Na+ [M+Na]+: 511.3394; found: 511.3394.

Analogue 7: Method K2 with DMSO (41 μL, 523 mmol), SO3 .‐pyr (25 mg, 157 μmol), DIEA (37 μL, 209 μmol) and alcohol 48 b (43 mg, 52 μmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Crude aldehyde in tert‐butanol (2 mL) and 2‐methylbut‐2‐ene (0.2 mL) with NaClO2 (15 mg, 167 μmol) and KH2PO4 (29 mg, 209 μmol) in H2O (2 mL). Work‐up NaCl (4 mL) and CH2Cl2 (20 mL). Crude carboxylic acid and HF.‐pyr stock solution (0.50 mL, out of a solution of THF (1.3 mL), pyridine (0.75 mL), HF.‐pyr (0.25 mL, 75 % HF)) in THF (1.0 mL). Work‐up NaHCO3 (10 mL) and CH2Cl2 (20 mL). Chromatography (SiO2, CH/EtOAc, 3 : 2) gave the corresponding seco acid (12 mg, 17 μmol, 42 % over 3 steps). Directly used with MNBA (29 mg, 84 μmol) and DMAP (14 mg, 117 μmol) in CH2Cl2 (6 mL). Seco acid diluted in CH2Cl2 (8 mL). Work‐up buffer (pH 7, 10 mL) and CH2Cl2 (25 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the macrolactone (9.8 mg, 14 μmol, 83 %). Directly used with HF.‐pyr (0.5 mL) in THF (0.5 mL) and pyridine (0.5 mL). Work‐up buffer (pH 7, 5 mL) and EtOAC (20 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 7 (1.6 mg, 3.4 μmol, 24 %, 8 % over 5 steps). R f=0.28 (SiO2, CH/EtOAc, 2 : 1); [α] =‐24.7° (c=0.15, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.53 (dd, J=16.0, 4.0 Hz, 1H), 6.35 (dd, J=15.3, 10.7 Hz, 1H), 5.93 (d, J=10.8 Hz, 1H), 5.69 (dd, J=16.0, 4.9 Hz, 1H), 5.64 (s, 1H), 5.60 (ddd, J=13.8, 9.6, 5.3 Hz, 1H), 5.16 (d, J=9.9 Hz, 1H), 4.39 (s, 1H), 4.28 (ddd, J=10.8, 8.7, 4.4 Hz, 1H), 4.04 (ddd, J=10.1, 6.8, 4.6 Hz, 1H), 3.53 (d, J=9.2 Hz, 1H), 3.24 (td, J=8.9, 2.4 Hz, 1H), 3.18 (s, 3H), 2.48–2.43 (m, 2H), 2.26–2.15 (m, 3H), 1.89 (d, J=2.7 Hz, 3H), 1.87–1.84 (m, 1H), 1.76 (d, J=3.1 Hz, 3H), 1.64 (d, J=2.9 Hz, 3H), 1.51–1.42 (m, 4H), 1.25–1.13 (m, 4H), 0.80 (d, J=6.7 Hz, 3H), 0.55 (d, J=7.2 Hz, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=δ 173.6, 134.4, 133.8, 132.3, 132.0, 131.4, 130.9, 129.2, 128.5, 128.1, 128.0, 89.3, 76.3,73.2, 62.9, 55.9, 40.9, 40.2, 35.2, 33.8, 32.3, 29.9, 26.1, 25.5, 24.5, 19.8, 17.3,11.4, 10.5; HRMS (ESI+) calcd for C29H46O5Na+ [M+Na]+: 497.3237; found: 497.3237.

Analogue 8: Method K1 with DMSO (20 μL, 208 mmol), SO3 .‐pyr (13 mg, 84 μmol), DIEA (20 μL, 112 μmol) and alcohol 47 b (21 mg, 28 μmol) in CH2Cl2 (3 mL). Work‐up NaHCO3 (3 mL) and CH2Cl2 (20 mL). Crude aldehyde in tert‐butanol (2 mL) and 2‐methylbut‐2‐ene (0.2 mL) with NaClO2 (8 mg, 89 μmol) and KH2PO4 (15 mg, 111 μmol) in H2O (2 mL). Work‐up NaCl (4 mL) and CH2Cl2 (20 mL). Crude carboxylic acid with K2CO3 (11 mg, 84 μmol) in MeOH (2.0 mL). Work‐up NaHCO3 (2 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 3 : 2) gave the corresponding seco acid (9.5 mg, 13 μmol, 46 % over 3 steps). Directly used with MNBA (23 mg, 66 μmol) and DMAP (11 mg, 92 μmol) in CH2Cl2 (5 mL). Seco acid diluted in CH2Cl2 (7 mL). Work‐up buffer (pH 7, 3 mL) and CH2Cl2 (15 mL). Chromatography (SiO2, CH/EtOAc, 50 : 1) gave the macrolactone (7.1 mg, 10 μmol, 77 %). Directly used with HF.‐pyr (0.3 mL) in THF (0.5 mL) and pyridine (0.5 mL). Work‐up buffer (pH 7, 5 mL) and EtOAC (20 mL). Chromatography (SiO2, CH/EtOAc, 10 : 1 to 5 : 1) gave 8 (2.1 mg, 4.4 μmol, 31 %, 11 % over 5 steps). R f=0.44 (SiO2, CH/EtOAc, 2 : 1); [α] =‐8.0° (c=0.20, CHCl3); 1H NMR (700 MHz, CD2Cl2): δ [ppm]=6.59 (d, J=16.0 Hz, 1H)., 5.71 (ddd, J=15.9, 4.6, 0.7 Hz, 1H), 5.64 (s, 1H), 5.37 (ddd, J=9.3, 5.4, 1.6 Hz, 1H), 5.18 (dq, J=9.9, 1.3 Hz, 1H), 4.46 (s, 1H), 4.11 (dt, J=10.8, 6.0 Hz, 1H), 3.99–3.95 (m, 1H), 3.42 (d, J=10.0 Hz, 1H), 3.24 (td, J=8.8, 8.3, 2.2 Hz, 1H), 3.16 (s, 3H), 2.30 (dt, J=14.6, 6.8 Hz, 1H), 2.24–2.18 (m, 3H), 2.05 (dtdd, J=14.1, 6.4, 5.1, 1.3 Hz, 1H), 1.89 (d, J=1.4 Hz, 3H), 1.87–1.83 (m, 1H), 1.76 (dd, J=1.5, 0.8 Hz, 3H), 1.62–1.56 (m, 4H), 1.51 (t, J=1.2 Hz, 3H), 1.27–1.18 (m, 8H), 0.81 (d, J=6.7 Hz, 3H), 0.57 (d, J=7.1 Hz, 3H); 13C NMR (176 MHz, CD2Cl2): δ [ppm]=173.3, 134.3, 132.9, 132.6, 132.0, 131.4, 130.6, 128.4, 127.9, 89.6, 76.7, 72.8, 64.0, 55.4, 40.5, 39.9, 35.1, 34.0, 29.6, 28.1, 26.9, 26.8, 26.0, 25.5, 24.4, 19.7, 17.5, 11.1, 9.7; HRMS (ESI+) calcd for C29H48O5Na+ [M+Na]+: 499.3394; found: 499.3394.

MTT assays: The test compounds were investigated at human 1321 N1 astrocytoma cells using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay in order to assess their cytotoxic effects. Assays were performed as previously described by Baqi et al.30 In brief, cells were detached from the 175 cm2 culture flasks in which they were grown and subsequently counted using a Neubauer haemocytometer. Then, they were resuspended in the growth medium. An aliquot of the cell suspension (180 μL) was added into each well of a 96‐well plate to obtain 1000 cells per well and incubated for 24 h at 37 °C, 5 % CO2, and 95 % humidity. The outer wells of the 96‐well plate were filled with 200 μL of phosphate‐buffered saline (PBS) to prevent evaporation of the fluid. After 24 h, stock solutions (10 mM) of the test compounds (archazolids) were prepared in DMSO and diluted with cell culture medium to give tenfold of the final concentrations. Then, test compound solution (20 μL) was added to each well. The final DMSO concentration was 1 %. The cells were incubated in the presence of the appropriate drug for 71 h. Then, 40 μL from a freshly made stock solution of MTT in water (5 mg/mL) was added to each well, and the cells were incubated for 1 h at 37 °C, 5 % CO2. After the incubation time, the medium containing MTT was removed, and 100 μL of DMSO was added to each well in order to dissolve the crystals that were formed. The spectrophotometric absorbance was subsequently measured at 570 nm using a FlexStation (3 multimode plate reader, molecular devices) with a filter of 690 nm. The data were analyzed using Microsoft Excel and GraphPad Prism 5. Results were evaluated by comparing the absorbance of the wells containing compound‐treated cells with the absorbance of wells containing 1 % DMSO without any drug (=100 % viability). All experiments were performed in duplicates in at least three separate experiments.

P2X3 receptor assay. 1321 N1 astrocytoma cell lines stably expressing the human P2X3 receptor were utilized to determine the compounds’ inhibition of ATP‐induced calcium influx as previously described.13, 31‐32 The agonist concentration used corresponded to ∼80 % of its maximal effect. Full concentration−inhibition curves were determined, and IC50 values were calculated using GraphPad Prism. Data are means from at least 3 separate experiments, each performed in duplicates.

A. Membrane preparations of Chinese hamster ovary (CHO) cells expressing human A3ARs were obtained as described before.33 [3H]Phenyl‐8‐ethyl‐4‐methyl‐(8R)‐4,5,7,8‐tetrahydro‐1H‐imidazo‐[2,1‐i]purine‐5‐one ([3H]PSB‐11, 53 Ci/mmol) was used as a radioligand (0.5 nM). Nonspecific binding was determined in the presence of 100 μM (R)‐N ‐phenylisopropyladenosine (R‐PIA). The competition assays were performed in a total volume of 400 μL in assay buffer (50 mM Tris ⋅ HCl, pH 7.4). Stock solutions of the test compounds were prepared in DMSO; the final DMSO concentration was 1 %. The membrane preparations were preincubated for 20 min with adenosine deaminase 2 U/mL per mg of protein. Incubation was carried out for 60 min at 23 °C. The incubation was terminated by filtration through GF/B glass‐fiber filters using a 48‐channel cell harvester, and filters were washed three times with ice‐cold Tris ⋅ HCl buffer (50 mM, pH 7.4). The filters were transferred into scintillation vials and incubated for 6 h with 2.5 mL of scintillation cocktail (Beckman‐Coulter). Radioactivity was counted in a liquid scintillation counter. At least three separate experiments were performed. Data were analyzed using Graph Pad Prism version 5 (San Diego, CA, USA). For the calculation of K i values by nonlinear regression analysis, the Cheng−Prusoff equation and a K D value of 4.9 nM for [3H]PSB‐11 were used.

HLE assay. Assay buffer was 50 mM sodium phosphate buffer (pH 7.8) containing 500 mM NaCl. An enzyme stock of 100 μg/mL was prepared in 100 mM sodium acetate buffer (pH 5.5). A 50 mM stock solution of the chromogenic substrate MeO‐Suc‐Ala‐Ala‐Pro‐Val‐pNA was prepared in DMSO and diluted with assay buffer containing 10 % DMSO to a final concentration of 2 mM. In each cuvette, 890 μL of assay buffer were pipetted followed by 10 μL of DMSO (or inhibitor solution in DMSO) and 50 μL of the substrate dilution. The reaction was started by addition of 50 μL of enzyme solution. The final concentrations were as follows, substrate, 100 μM (=1.85 × K m); DMSO, 1.5 %; HLE, 100 ng/mL. The progress curves of product formation were followed at 405 nm and 25 °C for 10 min and analyzed by linear regression. IC50 values were determined from duplicate measurements by nonlinear regression using the equation v s=v 0/(1+[I]/IC50), where v s is the steady‐state rate, v 0 is the rate in the absence of an inhibitor, and [I] is the inhibitor concentration. Standard errors of the mean refer to the nonlinear regression analysis.34, 35

Full experimental procedures and copies of NMR spectra are available in the Supporting Information.

Conflict of interest

The authors declare no conflict of interest.

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Supplementary

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